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before you go grinding and cutting...
do you use the gun in 303?
if so is the HS correct for the 303 barrel?
if you answer yes to these questions then modify the 7.62 barrel by facing off the breach and running the chamber deeper. there is no sense in modifying the existiing HS if its correct for one of your barrels
also from your pictures I cant tell if you are headspacing off the case or the bolt stops.
As for HS - I did it with and without the cart. in the barrel also with and without the extractor (and shell) and the bolt locks in with NO movement either way. (what does that mean?)Quote:
Originally Posted by Mr E
As for grinding and cutting, I'm NOT going to do that. I'll either replace the locking shoulders or use a barrel shim as those steps are reversible. I'm not qualified to be cutting or grinding anything on this rifle (other than the wood perhaps)
Quote:
Originally Posted by djandj
you need to determine what is actually stopping the bolt it should be the case head but if its the bolt stops then you cant set head space
headspace is measured between the bolt face and the cartridge so stick in a dummy case and shut the bolt with out the extractor and see what gap you have between 1) bolt face and cartridge case 2) bolt and barrel 3) bolt and bolt stops and report back
with a case in and the bolt shut the bolt should not be touching 2 or 3
the bolt stops are only there to stop the bolt from flying out when the barrel is out and to stop the bolt from peening the barrel when the bolt is dropped on an empty chamber. they are not involved in any part of live firing
Many thanks Mr. E. You are quite correct. It appears that my rifle is not headspacing with the cartridge at all (see pics) The bolt stops with the bolt stops which are also aligned with the end of the barrel. The back end is held in by the shoulder stops. So shimming the barrel will not change anything for me (right?) It would appear that if we want to have a bit a play in the bolt back and forth between the stops (and barrel) and the Locking Shoulders we need to get a shorter licking shoulder (right?)Quote:
Originally Posted by Mr E
Here we see the bolt resting directly against the barrel an the stops
https://www.milsurps.com/images/impo...py2020Co-1.jpg
Here we see that even with the cartridge, the spaces between the barrel and the bolt face etc. don't change. The casing fits in the pocket created by the stops and bolt face.
https://www.milsurps.com/images/impo...py_zps5h-1.jpg
in both pictures it looks like the bolt is stopping on the barrel. can you fit a slice of business card between the case and the bolt face?
to me the issue looks to be zero head space...
back to Joe H
PS Joe is a guru when it comes to semiauto brens. he has helped me a bunch over the years
Quite right Mr. E. The bolt contacts directly on the bolt stops and barrel = 0 headspace since the locking shoulders allow for NO rearward movement of the bolt when locked in the shoulders.Quote:
Originally Posted by Mr E
What leaps out at me is the long casewall rupture at a point where it is --or should be-- supported. I suspect faulty brass.
M
Mike, the casing are steel (not brass). And they don't all fail. Just one in 60 or so. It appears to be some variance in the operation of the rifle. With essentially a zero headspacing, the current thought is that if there is ANY discrepancy in the cartridge or any unburnt powder or other fowling, there is no room for error possibly resulting in the rifle firing out of battery.
Quote:
Originally Posted by Joe H
Djandj,Quote:
Originally Posted by Joe H
Is this what is happening???? Use the feeler gages and determine what the amount of space is between the rear of the case and the face of the bolt which is stopped on the receiver lugs? Quote from above " If its .010" or better you may have problems. If its .015" plus IMO you definitely will have a problem." The bolt should bear on the cartridge case. The receiver lugs (stops ) are there to prevent the bolt from battering the barrel.
If your assessment is correct and the bolt is stopping on the receiver lugs before contacting the case just as Mr. E posted the gun cannot be properly head-spaced. In the current configuration the operational clearance which should be .002" + is zero.
Joe
Whoooooooa lads....... Let me stop you all there! The depth of the cart seating in the breech face of the '303" Bren gun is .055" to .059" and the MINIMUM acceptable CHS is .064". The breech block must NOT touch the breech block stops (the BBS's) when a round OR CHS gauge is in the chamber. This difference (between .059 and .064 is the reason why, if you use barrel washers to bring the barrel forwards a tad, you can only use two, up to a max of .006"..... get it?)
The purpose of the bbs's on the .303 gun are to STOP THE BREECH BLOCK from slamming into the face of the barrel when it's dry fired. This is WHY, when the breech block is closed on an empty breech, there is a running clearance between the rear of the breech block and the locking shoulder of (forget it now but it'll be something like .005" or so.....) But you get my drift!
What I am minded to suggest DJ does is set his gun up to the old Bren CHS of .064" GO and .074" NO GO by changing locking shoulders to suit. I am sure that the 762x54R CHS won't be far removed from this! Rimmed cartridges are more tolerant to CHS variables for many reasons*.
But while CHS is under discussion in this thread, I'm not convinced that it is the cause of the blow-jobs - or blow-outs! I'm convinced that they are caused by steel case failure every so often.
Nor am I convinced that the gun is firing with the breech partially closed. Guns that have had genuine breech explosions, such as SA80's and the odd GPMG, caused by user error, have catastrophic failures due to the explosive effects of the full load. As opposed to DJ's where the magazine blew off due to what is best described as a severe leakage of gas. In fact I mention a classic case regarding a Bren in 'the book' which I am now actively pursuing as we speak.....
Even for a US spec s/a Bren to fire on an open or unlocked breech would be a s/a Bren manufacturers legal nightmare - or a lawyers lucky day - depending on where you stand of course. You know what they say........... If you don't make it foolproof, a fool will prove you right. It's called Murphys Law
Nope, CHS needs to be put right but with regards to the failure it's just a mildly contributory factor and we're getting well into mission creep in the meantime.........
If I'm understanding this statement properly... shall we consider one other possible variable in our equation?
"The depth of the cart seating in the breech face of the '303" Bren gun is .055" to .059" and the MINIMUM acceptable CHS is .064"."
As I understand it... The Breech block has also been machined to accept the 7.62 case head in this conversion... if it was inadvertently bored deeper and wider (wider being the only required modification for the conversion scenario - for the cartridge rim) would not replacing the bolt improve our dimensional conundrum? I'm wondering if the cartridges are seating some extra depth in the breech block face and allowing the breech block to contact the BBS.
A .303 barrel and .303 bolt and some locking shoulders is all that Djandj needs to set up the CHS per the last post's instruction - right?
the described blow out was at the extractor but it blew the mag apart. extractor is on the bottom and mag is on top. the only way it could blow the mag off is if the breach was open.
this could also be caused by the floating firing pin being too heavy and firing the primer while the bolt is still moving forward
Not quite. A .303 bolt would have to be modified to fit.Quote:
A .303 barrel and .303 bolt and some locking shoulders is all that Djandj needs to set up the CHS per the last post's instruction - right?
Nope...... the massive build-up of gas is instantaneous and it might have blown downwards UNTIL it will have met the top of the piston extension where the extractor cam is situated. From there, there'd be nowhere else to go and as a gas always takes the line of lease resistance it was deflected elsewhere........... straight into the body and magazine
Peter,
Every head spacing number I have given DJ is consistent with the Bren Gun Manual which is for the .303 British. Exactly what I have used for my Mk I & MK II semi builds. We are all saying the same thing about the receiver stops. The bolt should bear on the cartridge head not the stops. If, as we suspect, the bolt stops on the bolts stops and has no clearance between the bolt and LS it is clearly not set up correctly. Both cartridges are rimmed and are within .001" of the same rim thickness.
The bolt for the .303 if the rifle is head-spaced properly should work for the the 7.62. The only modification made to the bolt is machining a larger dia for the 7.62 rim. The bolt face should not be altered as Wally G noted. IMO the 7.62 should be set up with higher headspace standards than the .303 as the .303 case head makes it far more tolerant of loose headspace than the 7.62.
Until DJ tells us how much space is between the case head and the bolt face we really don't know if it is an issue. If its .005" the gun is not set up properly but headspace is not causing his problem. If its .015" then it is probably causing his problem.
I guess I still haven't made it clear regarding what my "out of battery" issues are. In the original FA Bren after the instant of firing the carrier has to travel about 3/8" -1/2" before the carrier unlocks the bolt. The instant the bullet passes the gas hole in the barrel the impulse from full gas pressure drives the carrier rearward. IMO the 1/2" -3/8" of travel is to allow the bullet to leave the barrel and barrel pressure to dissipate before the bolt unlocks. If the carrier is not fully forward there may still be gas pressure when the bolt unlocks. I have seen semi striker designs that could allow this to happen. The combination of drag on the return so that the carrier is not fully forward and a striker design that allows the rifle to be fired without adequate carrier travel could cause case blow outs IMO. This could never happen in the FA Bren
Joe
Quote:
Originally Posted by Joe H
Thanks Joe. As you can hopefully see in the pics, everything is lined up for an exact fit. There is NO space between the bolt and the stops (except along the upper part looks like I can get the .002 gauge in a little way - but then it stops further in) and No space between the cart. and the bolt. As near as I can figure it, the pocket formed is exactly the size of the round. (unless of course the round is out of spec...) Once locked in the shoulders, there is NO movement possible forward or back by the bolt.
Thanks Peter. I checked again and as near as I can tell there could be possibly be .001 space between the end of the cart. and the the face of the bolt. (can't get the gauge in that small an area).Quote:
Originally Posted by Peter Laidler
As for steel failure... well I suppose it's possible, but the steel of the casings which fails seems rather thick. Much thicker and tougher than a similar brass cartridge. If headspacing isn't the issue, and the MFG was right and it was the steel then why did the problem change when I sent it back to the MFG the first time. I sent it back b/c it was crushing the recoil springs as well as blowing out the shells. He replace the barrel and perhaps some of the internal parts. However with the old barrel and parts when they blew out, it did not affect the operation of the rifle and did not blow out the mag etc. Now when this happens (every 60 rounds or so), we get a massive amount of gas shot back through the receiver enough to blow out the steel mag and make it look like a piece of pop-corn. Ammo stayed the same.... changed parts in the gun and the problem changed. Logic would dictate that this is at least partly influenced by the gun. (no?)
Again, should there be a bit of movement forward and back by the bolt when locked in the shoulders? My bolt is absolutely locked against the bolt stops to the front and the shoulders in the back.
Thanks,
What's the next step(s)? A shorter locking shoulder and one of Joe H's strikers?
Djandj,
As I see it, assuming all your info. is correct, your Bren is far too tight. You should have .002" or .003" Above the spec rim thickness for headspace and .002" min for operating clearance. I'll throw this up for other comments. I would take a few thous off the bolt stops and .004" to .005" off the locking shoulder.
Think about this: With no operating clearance between the bolt and LS as you fire 60 rds the bolt becomes hotter and harder to close causing the carrier problems moving forward. The sides of the receiver also get hotter and hotter but they can dissipate the heat faster. Just a thought :D
Joe
Thanks Joe - definitely along the same thinking that I had. It's just too tight in there. The bolt has NO movement in it and is resting directly upon the bolt stops and the shoulders. There is really no space to mention between the back of the cart. and bolt face. It APPEARS to me that there is essentially a zero headspace.Quote:
Originally Posted by Joe H
So.... who wants this monster.... Whom can I send it to for the proper headspacing and detail work?
dandj,
Check your PM's. Remember in the US whoever you send it to must have the proper Federal Firearms License (FFL).
Joe
Attachment 62429
What is this?
Several years ago Dan Shea from LMO asked me if I'd get together with a couple of Bren fiends in the US and do a 3 day Bren technical seminar, ending on the Sunday with a Bren shoot. I wish he'd followed it up. It is definately needed and feel free to slap me down, but some of the innermost intimate technical details seem to be in short supply where they're needed most
We should do one here in South Carolina Peter. We'll have to discuss it as LMO's plan was to do it in conjunction with the release of the book.
good eyesQuote:
Originally Posted by Vincent
what is that?
dandj take the barrel out and see what that chunk is
I was using blue painter's tape over the spent primer to test whether the firing pin would engage with the charging handle pulled back at certain points. I started using live primers with bullets and powder pulled, but got tired of killing perfectly good ammo. I realized I could do the same thing with blue painter's tape over the spent primer to see if a hole was made by the firing pin. That appears to be a bit of tape. I went back to find it, but it is gone. (it was not present during any of the problems.Quote:
Originally Posted by Vincent
Great eyes though guys.
We used to tests like that with spent cases, deprimed and the primer pocket filled with soap or kids plastercine. Or an Armourers dummy cartridge does the same thing
OK Having spoken to several experts referred to me by you kind folks as well as all of your posts herein, it would appear that the next logical course of action on this would be to get a shorter locking shoulder from BRP. I will endeavor to do that. Install it and losen things up on the bolt and see what difference it makes. I will faithfully report back.
Thanks again all.
Ok Gang - I took out the locking shoulder and measured it. .8175. So, now I need one about .005 shorter. BRP doesn't have one. Checked in with Sarco (no response yet). Any of you builders have a shoulder measuring about .812 or so? If not, I may need to send it out to someone to have mine machined down.
Thanks guys.
Don't do anything yet DJ as I have an answer but it's long winded so will come in early tomorrow morning!
was this what you were refering to?Quote:
Originally Posted by Peter Laidler
went and measured my sparesQuote:
Originally Posted by Peter Laidler
786
803
822
Thanks Mr. E. Nothing close enough. Appreciate you looking for me.Quote:
Originally Posted by Mr E
---------- Post added at 09:27 PM ---------- Previous post was at 09:22 PM ----------
No worries Peter. No luck in finding the right size anyway (at least as of yet)Quote:
Originally Posted by Peter Laidler
Thanks,
Try going out and buying 100 rounds of GOOD QUALITY 7.62x54R with brass cases and try firing it. I'd bet you don't have the problems that you're having with the crappy steel cased rubbish. I believe Privi Partizan makes it.....
That was it MrE. I knew I'd written it up somewhere.
Once again the CSM says what others might be thinking - that this ain't a CHS problem but an ammo problem. But being an Armourer I would blame the ammo instead of the gun of course. Great car number plate CSM!
I think that you can carefully stone the locking shoulders that you have - or the rear locking bent of the breech block. You just need a .003 or so running clearance. But please try. Different i8n an Armourers shop as we had a big tray of locking shoulders. But as I said above (thread 131) we didn't box them by SIZE but by largest through to smallest! I certainly have stoned the rear locking bent of an L4 breech block in order that I could compromise in the fitting of two perfect barrels where no barrel washers were allowed.
I know some have concerns regarding the quality of the commie ammo. I also know the people posting on another Forum consisting mainly of semi builders have used the ammo in their semi-Brens without the problems djandj has experienced. There have been instances similar to djandj's and all have been tracked back to headspace problems.Quote:
Originally Posted by Peter Laidler
As Peter noted above let Djandj get his Bren set up properly then if he still has the problem then maybe we can point our finger at the ammo.
C130Pilot's friend Joe has a FA Bren converted to 7.62x54r, not surprising considering the cost of ammo. C310 posted a video on this Forum showing the Bren in operation. Initial problems were too much gas and mag feeding. I know both problems were solved. Smaller gas orifice and a mag that worked with 20rds. IMO if you can get a FA to work on 7.62 it ain't the ammo :D.
Joe
I was told the Historic Arms Bren uses an unmodified breech block. And there’s no shortage of them here. So… I am wondering if stoning the breech block is an option?
Djandj would have to replace the firing pin, but that’s much easier than replacing the locking shoulder.
Dandj,
Removing .004-.005" off the LS (or off the back of the bolt) will be a real pain in the a-s to do by hand, but probably the safest way, if you are not comfortable with setting up and using high speed machinery. You will need a perfectly flat surface, I use a piece of plate glass and some emery paper or a good flat stone.
I would do the LS. If you can get access to a disc sander (grinder) it will take just a few minutes. If the table can be rotated, depress it 25 degrees, if not make a ramp out of wood or whatever so that the LS bottom face sits 25 degrees above horizontal. Use the cross cut slide to keep the LS square with the disc and the jig or depressed table to get the correct grinding angle. Before starting be sure the face of the LS is perfectly flat with the disc.
You can refer to the sketch of the LS I previously posted on this thread if you want to check the angles.
Just touch the LS to the wheel, don't push hard, you only want to remove about one thous each time you touch the disc and you don't want to heat up the metal so that it changes color. Constantly check the dimension till you have the correct length. The difference between what you want to grind off the face will be the same as the difference in overall length. The effect of the angle is negligible. I'd shoot for .8175 - .004 = .8135" . You can always grind more off but you can't add any:D.
Joe
We used what we called 'three corner stones' to stone down shoulders and the like. Not too difficult and once you get going it doesn't take too long. I have done countless No4 cocking pieces, sears etc etc including L1A1 locking shoulders. Plus the odd Bren too of course.
We also regularly stoned back the breech block face if it contacted the barrel while checking CHS.
I'm not sure that you can use an unmodified .303 breech block because the 762x54R has a slightly larger base rim diameter and won't fit into the cart seating.
Ah! I forgot about the larger rim.
IMHO, it is FAR easier to weld up, or take down, the BOLT locking surface. You'll need a coolant-flow grinder to take it down, but it does work well.
Same thing with moving it up (tightening) the lock-up; You can weld up the rear locking surface and the grind to fit the specific locking block in the gun.
For my original select-fire BREn, I am in the process of making two caliber conversions- one, 8mm using one of the mystery re-bored and chambered original .303 barrels that are floating around out there, and two, a .308/7.62mm NATO conversion using an SA 7.62mm barrel. Both conversions will use standard, original .303 bolts with 7.62mm extractors installed. (Magazines are ZB26/30 mags for the 8mm, and ZB-39 mags for the .308. The ZB26/30 mags require a slight opening up of the rear mag well area.)
Both barrels are fitted to lock up tight and smoothly in the barrel recess in the receiver; at that point, current (-ANY-) "headspace" of the chosen bolts with the installed locking shoulder is irrelevant as each bolt will be hand fit to mate properly with it. The goal is to make each conversion such that all that is required is to field strip the gun, exchange the barrel, bolt, and magazine, leaving the installed locking shoulder and all else in place.
As mentioned above, each bolt will have a small amount of weld built up on the bolt locking surface, then ground down to the final fitment. Thus , each bolt is thus "fully committed" to the specific conversion/receiver combination, but since bolts are cheap and available, I judged this the best course of action.
(I have also a 7.62x54R conversion "mostly" done, as I have previous mentioned, though am currently stalled on the magazine.....I have decided the only rational plan is using a modified DP-28 47rd pan, modifying the underside receiver interface to fit and lock in the BREn receiver. Got most of that done, but will still be awhile to get it fully fitted.)
-TomH
Thanks guys. I do want to get the rifle set up correctly first before I blame the ammo. IF it is firing out of battery or whatnot, using weaker brass casing than the steel will not help. Steel is WAY stronger than brass. If I am relying on unsupported brass to contain a .30 explosion, I'm nuts.
As for the shoulder, seems like most folks agree machining is necessary if I can't find one the right length. (and not having much luck so far) I don't have the necessary equip. and experience. But I will be happy to ship the shoulder and compensation to those who do (and can do it rather expeditiously).
Any volunteers?... Any conscripts?
Thanks,
It will not be a sure thing... but I'd contact Mark Graham.. of Arizona Response Systems... he's a really good guy and one heck of a fine gunsmith... I know he has the shop and know how to do this work... but a semi Bren is not his normal subject matter. He is highly regarded as an AK and FAL builder and the FAL uses a locking shoulder for CHS... so I'm confident of his ability. He might want to read this thread to get some context of what you are up against and the expert commentary provided on the possible solutions.
Aside a bit DJ and your comment on brass v steel case. Then yes, steel IS stronger than brass as a material BUT we are talking about steel v brass in an APPLICATION of a metal. I usually follow up with a car related engineering example but can't think of one off hand except to say that brass is FAR more pliable and resilliant. And this is exactly what you need for cartridge cases. It is also a superb method of taking heat out of the gun (easy test for students to test, experiment with and write up.....) although this isn't a feature in this instance.
Near as I can reference without getting to exact specific alloys, the mild steel used to make cartridge cases has pretty much the same yield and ultimate tensile strengths as cartridge brass. If the steel wasn't of very mild alloy, it would not take the deep draws required to form the finished cases.
Tom,Quote:
Originally Posted by TactAdv
To make a longer LS I was thinking about adding weld to the LS and grinding back but had the same reservation about welding on the hard bolt, cracking. I just ended up making a new LS.
Have you tried welding the bolt yet. Technique and type of rod?
I've done the same conversions for my semi MK II. I had a .303 barrel re-bored and re-chambered for 8mm Mauser with headspace set so that the rear face of the case was in the same location as the rear face of a .303 British rim.
I have done the 7.62 x 54 r conversion. The converted bolt also works and headspaces with the .303 British. The 54R bolt also works with a ZB39 barrel and the 8x56R. The 54R mag issue is another story. I have a few ZB39 mags. I found one the works with 20rds of 54r:confused: , the rest will only work with about 13rds. By using a helper spring, annealing a few leaves of the leaf spring, and some other mods. I was able to get reliable feed of 25rds of 54R in the ZB mag.
My 54R bolt also headspaces with the 7.62 x 51 Nato and the 8mm mauser. Interestingly either will cycle with the standard .303 British extractor. Haven't live fire tested yet they hand cycle reliably :D .
Maybe I got lucky, hopefully, just change barrel and mag for different calibers. My bolt and Locking shoulder works for all.
I also noticed that the 20 rd ZB26-30 mags will only work with 19rds semi-auto. With 20 rds they have no space left for the bolt when retracted to push cartridges up further in the mag. 20 rds for FA open bolt only :eek:
Joe
Djandj,Quote:
Originally Posted by djandj
Just do it yourself with a stone or emery paper and a flat surface. Yes it is a bit tedious the first time. Easily less than an hour and as Peter said easier as you get the hang of it and its pretty difficult to screw up by doing it by hand:D.
Joe
I think a brass case is actually hardened and stronger as a result of cold hardening when the case is formed. The case neck is always annealed (heated and left to cool) so it is softened and will not split. This is the discoloration you see on the case necks of military ammo. Commercial manufacturers usually polish after annealing so you never see the discoloration. The case head is left hard and should never be annealed.Quote:
Originally Posted by jmoore
Joe
:thup: And it helps the case obturate when the round is fired.Quote:
The case neck is always annealed (heated and left to cool) so it is softened and will not split.
I never thought of steel as better or stronger than brass for cartridges. I always viewed it as a poor second or substitute. It's not really steel anywayzzz...it'll be a softer mixture.
That's a very valid point BAR. On the same track, then surely if steel was as good as brass, we'd ALL be using it. But it's not. As you say, a reasonable good substitute.
I say that DJ ought to at least try a mag full of brass cased stuff, even if it is to eliminate the steel case proble.
Incidentally DJ, did any of the successfully fired steel cases show signs of belling outwards at the unsupported extractor way part?
Joe, Yes on the bolt weld. Did one so far. Only the locking area seems hardened to any great degree. I did not pre-anneal. I am going to actually send out my other bolts to a trusted friend, who is much better set up for these than I am.Quote:
Originally Posted by Joe H
TIG-ed, using my favorite old standby rod "Super Missile Weld".
Super Missileweld | The Harris Products Group
Only because I have access to it, I used a CNC surface grinder. One could also mill, or stone grind, or use a power wheel if you can get a good fixture for the proper angle presentation. Your only building up a VERY small amount, and taking back down even less, heat input control is the game, so go slow both ways.
Thanks Peter. As far as the casings go, when things go well, they go very well. NO signs of bulging or undue wear of any sort. (until things DON'T go so well) That's the maddening thing. If the steel weren't good enough, then ALL (or most) of them would fail. One in 60 or so is a different story. As for using brass, that is another option. I saw a sale on Yugo brass surplus 54R for about .33 each. I could do that. Of course, it still defeats the purpose of having the bloody thing built to shoot Soviet 54R surplus to begin with. Furthermore, IF the rifle is firing out of battery as we suspect, merely changing to brass won't solve the problem. But point well taken, it WOULD eliminate the ammo from the equation as a factor.Quote:
Originally Posted by Peter Laidler
Those are stick welder electrodes. Here are the TIG rods 3SMW | The Harris Products Group
Yup, Mea Culpa. I just quick searched the name. ;-0Quote:
Originally Posted by Vincent
Thanks Tom for the Heads Up on the Super Missile Weld. I'll get some TIG rod and see if I can save my very short LS from the scrap heap:DQuote:
Originally Posted by TactAdv
Joe
OK gang - while I am awaiting either a shorter LS (or someone to properly grind down mine), I ordered a bunch of Yugo surplus (brass case). I'll take it back out and see what happens. This way we will eliminate the ammo as a variable. (and either give me or the ammo was the problem crowd a big told you so)
I'll report back in a couple of weeks.
Thanks,
When you're putting the LS back in DJ, don't forget that it doesn't need to be tightened like Jumbo/747 wheel-nuts. It's just got to be hand tight.
(Some senior Armourers used to say that the screw should only be finger tight in order to allow the shoulder some degree of articulation. I don't agree with that because even if it's hand tight, the screw is additionally retained in place by the screw being staked). Additionally don't forget that it's not the screw that takes any of the recoil load. It's the rear surface of the LS that is tight up against the recess in the body that takes the shock of discharge and spreads it along the gun body.
Getting off the subject a bit, but you'll find that the screw is a bit of a sloppy fit in the screw hole. All the best with the brass cased ammo trial. I'm keeping my fingers crossed
I will look through a big box of LS's next week to see what sizes are there so don't fret if you can't find anything locally
Have you compared the Super Missile rod to 309 stainless? Quite a few people think that is what it is.
Thanks Peter. We'll see how it goes and report back.Quote:
Originally Posted by Peter Laidler
Steel is CHEAPER as a material but its physical characteristics require that all of the case-forming tooling be Tungsten Carbide.
The Soviets, having limited domestic supplies of copper and zinc, (better used in electrical equipment than being sprayed all over the steppes), but the lion's share of the world's Tungsten supplies and, somewhat importantly, a "command economy" took to steel cases for EVERYTHING from pistol to artillery sized cases.
Their "satellites" and fraternal cousins followed suit.
The US produced a sizable quantity of steel-cased small arms ammo as well during WW2 as they also have Tungsten and "the technology". Somewhere in the cartridge "collection" are a few steel-case .30-06 and .45ACP rounds of US origin.
Carbide was better employed for MAKING ammo rather than BEING ammo.
Good points. But I think Tungsten Carbide does have a place in ammo.
1 Inch Steel Plate vs two shots Armor Piercing Bullets - YouTube
I have .45 ACP and .30 M1 ammo with steel cases. I never cared for it as it stresses the extractors too much. Extraction can already a be weak point with weapons so why compound the problem.
Sorry to say but I can't see the logic in that Brian. The extractor still has to ride up and over the case whether it's made from steel or brass. And it still has to withdraw it too. Or have I missed something in the reading.
No, I agree with that logic but I always felt that brass had a lubricity that steel does not. The M1 Carbine's extractor is not the most robust design in the world either. I know steel casings aren't good for AR type rifles but most of those problems have been cured with the SOCOM mods to beef up the extractor power. Buildup of lacquer in the chamber can be a culprit too if not thoroughly cleaned. Just problems I've seen/cured here as many are using Wolff and other brands of steel cased ammo in quantity. Bear in mind that some don't exactly put weapons maintenance at the top of their priority list either. I don't think steel is a problem with most MG's.
Steel .45 cases have always extracted harder for me as well. Haven't noticed so much with 9x19, but that's probably due to the .45s being in finer tune for various applications, ie. light bullseye loads, Steel Challenge "go fast" loads, full power ammo, etc. Used to reload steel cases quite a bit for the .45 as that's what I had the most about the house.
I think the real virtue of brass cases is it's ability deform considerably before failure. Steel might stretch 10-15% but brass may go 50%+ before it lets go altogether. Seem to remember an article in the back of Cartridges of the World, 8th Ed. (I think!) that covers the brass issue well.
17 pages and still going. Is this a forum record for thread length ?:madsmile:
I have to say that it's been interesting for me particularly as it's taught me a lot about the US designs for semi auto Brens. Not just a lot..... but everyhting I know now! A great thread for cross pollination of ideas/thoughts etc
Is your avtar your actual car number plate CSM? I ought to change the '......home of MG cars' part of my logo because we are now being bombarded with adverts for the new type MG cars........... from China! Who ever heard of Morris Garages in China?
Change your settings...you'll get 5 pages. Then it's an easier read. Longer pages.Quote:
Originally Posted by csmarcher
My story regarding steel-cases ammo involves severe damage to a SiG AMT.
The steel-cased Bulgarian? and Chinese 7.62 NATO ammo does NOT "grip" the chamber the same way, NOR does it spring back the same way.
If you ever examine brass cases tossed out of a SiG or a H&K 91, for example, you will notice a series of dark "stains" along the front two thirds of the case. (16 for a SiG and twelve for the H&K).
The brass under these stains is RAISED above the normal fired case surface.
What happens is that the brass starts to "flow" into the flutes in the chamber at peak pressure, momentarily "gripping" the chamber a bit harder, (remember we are talking about "semi-locked mechanisms here).
Then, as the bullet moves up the barrel, the pressure drops enough for the case to "relax" slightly, contract a tiny bit and allow the gas, still at relatively high pressure, to bleed between the case and the flutes, thus starting to "float" the case.
The cumulative rearward forces exert pressure on the front of the bolt assembly. This in turn acts on the "wedge" that holds the rollers in place, and under extreme mechanical disadvantage, forces the wedge, and thus the carrier to move rearwards.
This system was first used on the old German StG 45, VERY late in WW2. It was designed around STEEL-cases 7.92 x 33 ammo.
HOWEVER, unlike the StG 45, the mechanism of the SiG was specifically designed to operate with BRASS cased ammo, first in an experimental job that used a special short cartridge, and then in the Stg57.
The AMT, or at least its "military variant" is just a "NATO-ised" 57, for export.
Firing steel cased ammo in one of these is a recipe for disaster. The steel does NOT "flow" fast or far enough to provide the essential "grip" on the chamber wall, and thus, starts to open too early. The result is that the working parts move rearwards too soon and too FAST, thus damaging the rifle internally. There is also NO guarantee that said ammo is anywhere near the pressure curve and PEAK pressure as specified for "real" NATO fodder. Some will have noticed that our Chinese cousins even made steel-cased "7.62 x 51 NATO" ammo, complete with the NATO "Circle X" mark; not sure who they thought they were fooling.
It is POSSIBLE that a change of "wedge" angle and / or return spring may solve that issue, but who has a couple of "spare" rifles for the experiments?
Remember also that, post WW2, the Stg 45, and designer "retired" to Spain for a little Rest and Re-Development. The result was the CETME series that started out with its own "special" cartridge and moved up to a "mildly" loaded 7.62 NATO case and ultimately went back to Germany to become the G3, firing "full-strength" NATO ammo.
Whilst both the SiG and the H&K rifles use mechanisms derived from the same grand-parent weapon, they are quite different to fire. The recoil of the SiG has a smooth, "rolling" push, whereas the H&K has a distinct "jab".
Back when Oz still had a sense of humour, I had both types and loved them dearly; The SiG for its pleasant and precise shooting and the H&K for its robustness and ability to handle dust and dirt, (and the fact that I had the proper scope for it).
If you own a SiG AMT, (lucky you), "cheap" ammo may ultimately be VERY expensive to use.
This marvel of engineering relies heavily on the ammunition, (too heavily in my humble opinion). It must be made just right. Any variance can, and often does lead to the case becoming stuck in the chamber. If the case is annealed too much or too little, or not enough area or too much area is annealed, and heaven forbid you use commercial ammunition that’s not made to the exact dimensions demanded by the engineers. And then there’s the type of powder………Quote:
Originally Posted by Bruce_in_Oz
H&K’s fluted chambers are notorious for stuck cases. The Sig’s chamber flutes are not as deep, so it’s a bit more tolerant of different ammunition. But the whole fluted chamber concept adds a degree of complexity that’s not necessary and reliability suffers as a result.
A hard extracting, over gassed long stroke piston gun will run like a top on any ammunition. Yes, it’s crude. There’s no fancy over engineering, just brute force extracting the case. But who can argue with the reliability of the AK and PKM? And while not as over gassed the FN MAG, M1 Garand and the Bren are some of the most reliable guns in the history of warfare.
Some guns are like fancy cars that need high octane fuel or they won’t run right. There’s nothing wrong with cheaper low octane fuel. They are just not made to use it. Putting steel ammo in a Sig or H&K is like putting low octane fuel in a fancy car. If you want burn that stuff, you need something like an F150 pickup that’s designed to run on it.
The Bren was not designed to use steel ammunition, but it operates very much like guns that were and it’s certainly robust enough.
Attachment 62625Attachment 62626IMO Vincent is correct. Djandj’s problem is not a subtle problem of “flow” or fluted chambers as has been discussed in the brass vs steel argument.Quote:
Originally Posted by Vincent
The chambers on the .303 bren barrels are large. Just look at the bulge on the spent cases just above the base. The chambers were sized for reliable extraction, not reloading. I would suspect a 54r chamber that was that “generous” would result in problems directly related to steel vs brass but the .303 bren barrel converted to 54r has the correct chamber dimension beyond the neck.
After the discussion of the relative merits of steel vs brass for cartridges I would, of course, prefer brass. On the other hand steel has been used successfully for years mainly spurred by military use.
IMO the use of brass or steel really is not the crux of Djandj’s problem. He currently has some brass Yugoslav 54r to try. If its 182 gr I’m not sure how it will work in a Bren. Has anybody used 182gr in a Bren? If he tries it without any problems does it really tell us it is a brass vs steel issue? If the brass ammo has a deeper solid head like the .303 British, he may not have any problem. If it’s the same as the steel 54r, it will blow if it experiences the same conditions as the blown steel 54r.
To me the difference could be in the construction of the cartridge head. IMO the only way Djandj’s cases could rupture as his pics above show is that they are experiencing pressure after having moved to the rear, or are too far back when fired, and the thin walls have cleared the notch in the barrel. A short case head could cause this. This could easily be determined by x-sectioning one of the blown cases and comparing it with the good cases. This would be an ammo defect. Loose headspace could cause it but per Djandj’s analysis the HS is, if anything, too tight. Another explanation in a semi is that the bolt is unlocking too soon, the case if moving rearward before the pressure has dropped. Anything else???
My 2 cents,
Joe
What your looking for is what is known technically as the "coefficient of restitution" in metallurgical terms. Simply, it means to what amount does the alloy return to the original dimensions once it has been exposed to an expansive force, and then the force is relieved.Quote:
Originally Posted by Bruce_in_Oz
Overall, this is the discussion of "obturation". And you are quite correct in that many specific gun designs were specifically designed around a specific type of ammunition cartridge construction, and that random exchanged of case types does not always return the same results.
That said, tremendous amounts of effort were expended by, for example, the WWII German military-industrial complex to derive and provide multiple sources of ammunition supplies using differing constructions that were intended to be transparent in consumption by the end-user. This is NOT easy!
The issue TODAY is that it is almost impossible to determine, minus laboratory examination, all the relevant technical properties of commercially available fodder, so good sense is indeed best employed. The cheapest ammo is not always the cheapest end results as you found!
The interesting part about the "HK" details is that that specific action design relies almost entirely on INCOMPLETE obturation for proper functioning.....IOW's, if the case material is "flowing" into the flutes, that's a bad thing it is providing undesired resistance to functioning, the entire reason the flutes are there is "float" the case walls on high pressure gas and PREVENT complete obturation. Proper case material design DIRECTLY impacts that proper functioning, so random substitution of different case materials other than what it was designed around, is not good.
-TomH
---------- Post added at 10:27 AM ---------- Previous post was at 10:19 AM ----------
Quote:
Originally Posted by Joe H
PRECISELY, JOE!! He is experiencing PREMATURE extraction. As in other replies, the chambered dimensions are TOO LOOSE, there is insufficient obturation of the chamber walls under peak pressures, and the case is moving rearward under that pressure in an unintended fashion. Once the casehead base is exposed in an un-supported fashion, it fails.
"Resistance to movement", i.e., proper obturation under design pressures, is part of the design parameters for proper functioning.
A new barrel, properly chambered, will likely provide the intended functioning, although as this is a bastardized chambering job to start with, that is unclear.
I suspect that a combination of a previously well worn .303 chamber, combined with a well worn 7,62x54R reamer resulted in this particular barrel experience.
YMMV.
-TomH
Would make the reamer produce a smaller than standard chamber, not bigger.Quote:
Originally Posted by TactAdv
But not in the correct proportions. It is the mismatch in chamber shapes that is causing the lack of adhesion.Quote:
Originally Posted by browningautorifle
If the 54R reamer is cutting correctly it removes metal over the original dimensions; a worn 54R reamer does not do that, leaving the shape of the 54R case expanding into the bastardized partially cut .303 chamber causing INCOMPLETE surface contact.
A worn reamer.
-TomH
Whatever you think...
'BAR',
I would agree with you 110% if you were talking about virgin metal, but the problem is.....you have no idea what you are cutting with this arrangement of mismatched existing chamber, subsequently re-cut with a different reamer that isn't even really close to the original cartridge for over 50% of it's supported length.
A good example.......This exact same problem existed when Century Intl tried to sell a ton of 7.5x54mm MAS-56 rifles here that they "brilliantly" deduced could be "re-chambered" to 7.62 NATO by simply running in a 7.62 reamer sufficiently to allow the bolt to close. BAD IDEA. All of them suffered from the exact same problem we are discussing here. Century only had a couple reamers, and when they wore down, the guns so done got worse. Some came out so bad, they literally flew apart under pressure. The eventual diagnosis was precisely what I mentioned- incorrect, worn reamer in a well used chamber.
Just a data point for you.
Maybe we shopuld cross reference this bit of the thread to an idea being bandied about on the 'sleeving a .303" chamber' on the GUNSMITHING FOR OLD MILSURPS thread. Some interesting comments there that are/could be relevant here
I don't think there is a chamber reaming issue here. In the reaming process you are removing from .026" to over .030" (diameter) below the bottleneck the when a .303 is rechambered for 54R. Even with the .303 oversize chamber you are still removing significant material for most of the case length. In most conversions the neck is fire-formed into the double shoulder void as you can see from Djandj's spent cases. The double shoulder to the best of my knowledge has not caused any problems.Quote:
Originally Posted by TactAdv
The pics. below are spent cases from my semi Bren 54r on the left .303 British on right. The numbers are relative difference in diameter. You can see from the cases that the original Bren chamber is typically oversized. I drove a shaped plug into the .303 barrel before reaming so the 54r does not have the double shoulder.
Obduration - If steel can't form under pressure to seal the chamber how can the double shoulder be fire formed ? See Djandj's pic below.
OK gang - update! I shot 140 rounds of Yugo 182g lead core brass case ammo today.
for reference here is the stuff: Yugoslavian 1976 7.62x54r Lead Core Heavy Ball
Results? Well, NO blowouts! No case bulges. Some really deep extractor marks but nothing too bad. However, I did have some problems.
Below you can see, I shot only 3 steel cased rounds before I had a blow out. The brass round next to it was one of the first to really stick in the chamber after firing.
https://www.milsurps.com/images/impo...e1nxcuqe-1.jpg
https://www.milsurps.com/images/impo...dgcdg9z1-1.jpg
For the first 20 rounds or so = perfect. However, as the barrel and chamber became hotter - long about round 40-50, they began to "stick". Meaning they would fire but not eject. In fact the spent casing was "trapped" in the chamber and I COULD NOT pull back the bolt. Literally had to pull the rifle apart and then use a HAMMER to hit the charging handle to get the round out. However, NO bulges towards the rim, but the usual bulge up near the tip of the round. After a few of these I just let the rifle cool for 5 minutes and then ejected the casing normally.
I then increased the gas sequentially. Towards the end (and on the highest gas setting) it actually began to improve. Slowly the rounds would eject (or blurp out) or the gun wouldn't cycle but I could manually extract the spent casing without letting it cool.
Rounds 110 through 140 were almost flawless (save the misfeading from the mag every so often) or perhaps the spent case would slow the bolt down to the point it would short stroke and I'd have to manually charge it for the next round.
So.... we generally traded one problem for another (for now) Also: the yugo rounds were MUCH less accurate than the steel case stuff. At 25 yds and shooting from the bi-pod I could put 20 round through a dollar coin sized hole with the steel stuff, with the Yugo, it was more like a 2 inch spread at the same distance.
BTW - should I bother collecting the spent brass? Can it be reloaded?
So..... ideas? thoughts? comments?
It seems to me that with the brass cased stuff the 'coefficient of restitution' as described by TacAdv or just 'pliability' as described by me is showing its face. This stuff WILL adhere to the side walls of the chamber better (or worse for you of course.....) than the steel cased ammo. And this is JUST what it's doing.
However........ In a Bren, as the breech block is drawn down by the piston post to unlock, the extractor cam tightens up on the extractor and effectively makes it a solid part of the breech block. (it's not of course but is rigid to the breech block. Try it out of the gun to see what I mean.....) Simultaneously, as the breech block is dropping down while unlocking, it is rotating about the lowest point of the front face of the breech block against the breech block stops in the gun body. This draws/rotates the cartridge seating face slightly rearwards. This action just tweaks the thick rim of the old just fired and red-hot 303" case and breaks the taper seal of the case in the chamber. This is the primary extraction in the Bren.
My theory in your gun is this: The rim of the 762x54 case is much narrower than the .303" case and as such, during the primary extraction doesn't quite tweak the 762x54 case as much as it would the .303 case and therefore doesn't cause sufficient primary extraction or leverage on the stuck case.
We know this because you can still manually pull the red-hot stuck fired case out of the chamber using the cocking handle OR wait until it cools when it will contract naturally
Djandj,Quote:
Originally Posted by Joe H
I guess your trip to the range answered my questions. Did you fix the headspace issue?? I wouldn't reload those brass cases unless you have a 54r die with a double shoulder:D
IMO the 182 gr 54r is a long range sniper load for a rifle. I don't know of anyone who has used it in a Bren. The only experience I have is the steel cased "light ball". You may be in uncharted territory:D.
You might try to mike the brass case at the locations shown to see if the bass is bulged.
Does the Gun work properly with a .303 barrel ?
IMO you haven't "traded problems" its the same problem.
Joe
just pointing out that the steel he is using is heavy ball not the normal light ball that is normally used.
Why not just section several brass cases and find out what's happening inside for sure. No, I wouldn't reload that stuff. Perhaps a bit of chamber polishing will help? Couldn't hurt...
Thanks Joe. No I haven't touched the HS issue yet. No one seems to have the right sized shoulder (and I haven't found anyone willing to mill the .005 off it I need.). The question is "do I need it" With the change in ammo, it is no longer blowing up (although the sticking cases is a pain) Do you think the HS issue can affect the brass casing getting stuck in the chamber?Quote:
Originally Posted by Joe H
Djandj,
No matter how you slice it or dice it your Bren is not working properly on 54r ammo, either steel or brass cased. Since you had a steel case blow out on rd 3 I doubt the problem was caused by tight HS and heat.
The only other issue I can think of is the cycling problem. Possibly the bolt is opening prematurely because the carrier is not fully forward when the gun is fired allowing extraction before the pressure has dropped. Pretty easy to check but an issue that may be happening sporadically. Could be caused by a weak return spring or something else that causes drag on the carrier return. Before you pull the trigger turn the gun over, muzzle pointed safely downrange of course, and see if the carrier is in the correct position "A" relative to the bolt (see attached pic). You could also hand cycle with dummy ammo. The carrier should end up in Position "A" EVERY time the gun cycles. I found when building my semi that this was a problem to solve before any test firing was done. I think you mentioned in one of your early posts that you did have some recoil spring problems.
It is very difficult to diagnose a problem like this without actually getting your hands on the gun. You might try the gunsmith that Wally G recommended.
Other than that get a .303 barrel and if that works be content with .303 British
Joe
JUst been reading and digesting your thread 185 Joe and clearly we HAVE corrected the principle fault that DJ experienced. Brass cased ammo doesn't blow out and there's no sign in the photos that it is going to blow. I appreciate that others guns do work with steel cased ammo, but this one doesn't.
What is telling now is that the brass cases that don't blow out now make extraction difficult by adhering tightly to the chamber walls. Steel cases didn't stick - so by deduction, this tells us one thing. That the fired brass casings adhere to the walls of the chamber harder than the fired steel casings. There's nothing else that would cause the sticking.............
A bit of extra leverage during the primary extraction (PE) phase might help but we ain't got any more PE to help. So tto truly establish this DJ, this is what I'd do next. Slightly oil the brass cases before you shoot them and see how they extract now. If they still sticl like the proverbial 5--t to a blanket then it's a new, accurately re-chambered barrel time OR polish what you've already got.
Like Joe and others have commented throughout. iI's VERY difficult to diagnose a problem like this when it's not sat in front of you. But I'd say that the problem you have now, wqith brass cases sticking, is a LOT less than the original problem!
Peter,
Here is why I think Djandj's problem with both steel cased and brass cased ammo is the same problem.
Here is quote from a Hornady technical web page:
Link: Internal Ballistics - Hornady Manufacturing, Inc
Quote:
As the pressure continues to build, the case is forced so tightly against the chamber wall that it cannot move; but since we had a gap between the base of the cartridge case and the face of bolt or breech block - what we termed a little headspace - the case itself must stretch in the head region circled (above, right) to force the case head back.
As the case is moved rearward the primer is reseated in its pocket, when the bullet exits up the barrel the pressure drops, the case cools, and the brass contracts enough to permit extraction of the fired cartridge case from the chamber (left).
IMO in Djandj's Bren the steel case head blows out as it prematurely extracts, the brass case which is much more pliable and may have a better head design also prematurely extracts but does not blow out but still having pressure during initial extraction does not cool down enough to allow proper extraction.
My 2 cents,
Joe
I thought the Yugo brass case was heavy ball and his steel case light ball? :confused:Quote:
Originally Posted by Mr E
Here’s the picture of the ammo can from post 48.
https://www.milsurps.com/images/impo...nqjesdov-1.jpg
Am I reading the can wrong? 7.62, Light Ball, copper washed steel case, silver = steel core bullet, powder and ammunition produced in 1975, 440 rounds?
Just to add a little to the brass/steel debate. These steel cases have a copper coating, with maybe some zinc mixed in too. The coating acts as a kind of lubricant making the cases less likely to get stuck in the chamber.
Quote:
Originally Posted by Joe H
We agree totally, Joe! Your 2 cents is right on the money! This is just what i said earlier:
"..PRECISELY, JOE!! He is experiencing PREMATURE extraction. As in other replies, the chambered dimensions are TOO LOOSE, there is insufficient obturation of the chamber walls under peak pressures, and the case is moving rearward under that pressure in an unintended fashion. Once the casehead base is exposed in an un-supported fashion, it fails."
-TomH
Please tell me if I'm barking up the wrong tree but the blowing case problem has been solved by using brass cased ammo - surely. What the problem now is, is EXCESS obturation caused by the fired and still hot case sticking in the chamber. Additionally, the brass case is measurably hotter than a steel case. (We know this from student experiments). So there must be MORE cartridge obturation in the chamber. And being a tapered cartridge case, just the slightest tweak SHOULD break the taper seal. Think morse taper!
Unless the gun is working in blow-back mode, the bullet has to pass the gas port in the barrel before ANY rearward movement of the BB&PAssy can take place. And even then at the 60:1 ratio, the Mech Safety feature ensures that the bullet has long left the barrel WELL before the BB has unlocked.
I realise that I don't truly understand the semi 'rifles' so please feel free to berate me in any way you like. I take it all in good heart..........
Peter,
I think you nailed it with your “blow-back mode” comment.
Back in post 93 djandj said there was almost zero CHS and the gun would fire with the breach block NOT completely locked.
If the breach block is not locked, it’s logical that the gun would be operating blow-back mode and that is the cause of the “premature extraction.”
The mechanical safety doesn’t prevent this from happening with this semi-auto striker system design.
Well, you could conceivably get any number of problems that would cause the gun to fire OOB, in a form of API. Chamber obstructions, stuck or jammed FP, etc., all could cause enough primer contact to set off the cartridge before full dwell is reached. All manner of other semi-auto gun types exhibit this all the time.
One of the things I never liked in all these "semiauto machine gun" design conversions like the BREn, RPD, DP, etc is the necessarily very long FP's that are employed......lots of room to get stuff in there and cause friction or outright jams and these all have very long pin protrusions to begin with. If the FP tip is not fully retracted as intended.....for any reason.....coming round again it can easily function as a fixed FP, especially if the primer cup thickness is not very....thick, or you are dealing with an old and over sensitized priming composition.
Might not be a "steel versus brass case", argument there at all, might just be a very differing primer sensitivity between the two batches of ammunition, coupled with either a sticking FP, or the reverse situation, a long, heavy FP that is allowed to slam forward under inertia??
-TomH
Peter,Quote:
Originally Posted by Peter Laidler
Your statement above is absolutely correct for a Bren as they were originally built even in semi auto mode. The Bren is an open bolt MG and it is fired from an open bolt in either FA or semi. The piston post is the hammer that strikes the firing pin in either FA or semi mode. Since the piston post is part of the carrier it cannot touch the firing pin until the carrier is about 3/8" forward of where it unlocks the bolt. IMO the 3/8" is the distance the carrier should travel before the bolt unlocks allowing time for the bullet to leave the barrel and the pressure to drop before extraction. I have no technical proof of this.
In the US we cannot build an open bolt gun, it can be too easily converted to Full Auto (ATF Requirement). The striker fired semi auto (djand's Bren) separate the firing from the closing of the bolt so that the semi Bren becomes gun fired from a closed bolt.
After firing the gas piston operates the mechanism the same as the original Bren except that it has more recoiling parts to move (the separate striker) and it has to cock the striker spring. The return of the carrier & bolt may also have to deal with issues caused by misalignment as a result of the welded up receiver pieces. All our semi receivers are built from re-welded de milled Brens.
If on the return stroke the carrier stops short, for whatever reason, of the 3/8" forward of the bolt unlocking position and the rifle can be fired from this position IMO the bolt may unlock before the gas pressure has dropped to safe level. Or maybe the bolt never locked but in that case I think the results would be more catastrophic. The striker can be configured to eliminate this possibility by the lower part hitting the carrier if it is too far rearward and the upper tab not striking the firing pin. The takes both an offset striker tab and corresponding proper length firing pin to achieve this mechanical safety.
If Djandj's Bren can be fired without the 3/8" carrier travel it's my theory that he may be getting premature extraction. At least this is one thing to look at.
Joe
Quote:
Originally Posted by TactAdv
I understand those issues, but this makes me think it’s not one of them.
It’s happening with the first round, when the cocking handle, slot, etc, limits how far the breach block and carrier can be pulled back. This in turn limits the amount of energy stored by the return spring.Quote:
WOW Joe - you are way ahead of me on that. Yes, the gun does blow up usually on the first round of the mag (after manual racking).
But when a round is fired the breach block and carrier travel back a greater distance and more energy is stored in the return spring. So when the breach block and carrier move forward again they are pushed with more force than cocking can provide to lock the breach block.
Vincent,Quote:
Originally Posted by Vincent
Additionally Djandj is using some sort of plug in his mag since he is in California and mag capacity is limited to 10 rds. Since it is a 25 rd zb39 mag he would have to have a plug equivalent to 15rds so that his 10 rds are rd 25 to 15. The mag may be causing enough drag so the the bolt doesn't lock properly. Easy enough to check. Don't use a mag & see what happens.
Joe
Good point, Joe.
He could also flip the gun over after loading the first round from a magazine and see if the bolt is up and locked before pulling the trigger.
From what I have read about the Historic Arms semi-auto Bren guns, it seems to be a common problem for them to be very “tight.” My read on this (I could be wrong, so anyone who knows please chime in) is the receiver sections were not perfectly aligned when they were welded together. If that’s the case, there would be considerable drag on the carrier and that along with the zero CHS might be the problem.
--------
Very interesting post, Peter. The rotation explains why the rim looks like it has been twisted.Quote:
Originally Posted by Peter Laidler
Attachment 62860
In what dimension are you reporting systematic misalignment of receiver sections during weld-up? Define misalignment please.
That is a rather strong defect to be called out on here say... I have a good many of the HA guns and all welded mating surfaces on mine are flush and level... I know first hand that a jig is used for positioning during welding... and that the finished joints (internal and external) are machined flush with a milling machine. But I suspect that is not what your saying...
Using a jig etc. would not necessarily prevent some minor receiver warping due to heat and variable contraction... but I know heat sinks are used and applied weld beads are alternating short runs to minimize over heating and receiver distortion. I would not define the effects of variable cooling and heating expansion/contraction as a "Misalignment" defect. This is just the harsh reality of re-welding torch cut steel receivers - to be successful one must control and compensate for the inevitable expansion and shrinkage inherent in the process. When warping does exceed tolerance... you have to cut the sections/segment of weld apart and start over... or scrap the entire receiver. Someone who knew what they were doing would have to evaluate this receiver to see if it was in fact square and concentric about its center line/axis. If warped... function problems like these could result.
Since you are suggesting that a warped receiver could bind upon the reciprocating internals... intuitively this would make perfect sense to me... but over time I would think that this binding would lessen as the moving parts wear in... and any real/material binding forces would routinely prevent the loading and extracting functions which appear to be taking place successfully in this gun for many rounds fired. If the warping was truly excessive... the internals would not function at all... they would simply bind up. Such a gun should not have left the shop in the first place... as it would not pass a final test function firing routine.
As for the charge of systematically tight headspace in HA Brens... I have no knowledge of this regarding HA production methods... seems plausible... and I have not had the need to go about measuring my guns... but it would be an interesting sample to test as they were produced over the last 10 years - some many years apart. This gun being discussed certainly needs more CHS to be in spec - no doubt.
Ponder this... if as you postulate, the front gas cylinder is not in alignment with the gun's axis due to receiver warping... the gas piston might be hanging up/binding on it's last few millimeters of forward travel in the gas cylinder... especially with carbon buildup after many rounds fired and thus potentially preventing bolt lock-up... but if this is the case... the occurrence should be more often and much more regular... and progressively worsen with increased fouling.
However, much of this is just observation and speculation... only the gunsmith that has the weapon in hand is in a position to efficiently evaluate its function or malfunction. Yet, I've thoroughly enjoyed the mental exercises that these discussion points and counter points have provided.
I am not reporting it, other people are. Google and see for yourself. If I understand them correctly, it’s the x and y axis. X being the horizontal and y the vertical.Quote:
In what dimension are you reporting systematic misalignment of receiver sections during weld-up? Define misalignment please.
Read my post again. There’s no such charge. The owner of THIS gun says it has zero CHS.Quote:
As for the charge of systematically tight headspace in HA Brens...
Let’s keep it enjoyable then. I understand you have several HA Bren’s and like them. But there’s no need for you to try and put words into my mouth that I haven’t said.Quote:
Yet, I've thoroughly enjoyed the mental exercises that these discussion points and counter points have provided.
Quote:
Originally Posted by Vincent
Vince - that was the STEEL I was using. I later got the Brass cased Yugo and reported back with that.
Joe - just to eliminate the issue, the way I limit the magazine to remain CA legal is simply a wooden dowel cut out curved to fit along the back channel of the mag. It does not exert any pressure on the mag follower it just rattles around until the follower goes down to the 10th round and then stops the follower from going any further. As far as the pressure from the mag it is no different than putting only 10 rounds in a 30 round mag. (very little pressure)Quote:
Originally Posted by Joe H