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Here's a simple question to kick-start the 2015 forum and hopefully get the brain cells working into the New Year for you Bren Fiends out there. And it's this. .303" Bren breech block....... Anyone out there know why the .303" Bren breech block has two distinct protruding feed horns at the top. Not required on any of the others including the 7.92 or the 7.62 guns.
Don't be shy in coming forwards because the person who's thinking outside the box will probably be on the right lines
There has to be two as the ejector has to fit between them, and they must be wide enough to pick up the rims from the staggered feed. Additionally, the forward projection allows the rims an unobstructed passage down the face of the bolt as they chamber. The underside of the projections also acts as a positive shoulder for the rim to sit against under the pressure of the extractor, holding the fired case in position to be struck by the ejector, giving reliable ejection.
Not quite right Woodsy. It needs two horns, because the rounds feed alternatively from either side of the Mag. The underside 'Projections' have no bearing as a positive shoulder. As the case sits firmly on it's base in a recess. It cannot move up or down in the recess. So therefore, as a positive shoulder as you call it. That is superfluous!...
Now, go back to your desk & try again young man! see Me after school!........LOL ;)
good try though, well done buddy.
It must be something to do with the rim on the case as the 8x56r ZB39 has similar horns.
I did mention that the feed horns had to be far enough apart to strip the rounds from the staggered feed mag. I will now go and sit in the corner and have another think!Quote:
Originally Posted by tankhunter
I have just examined 3 of my breech blocks and the underside of the feed horns are precision ground to the correct rim recess diameter, so the underside of the feed horns does provide a solid support for the rim against the spring pressure of the extractor. It has been my long experience with many firearms that positive ejection is very much reliant upon good positive case support during extraction.
I also suspect that the horns contact the rear face of the barrel in battery and provide a pivot point to assist the piston to cam the rear of the breech block up into the locking shoulder recess.
That is my 2 cents worth anyway!
I'll come in towards the end of the month chaps. Good and valid points all round of course.
The pivot point for locking up Woodsy are the breech block stops. When these are eventually worn down by the battering (usually by the dopey training staff using SERVICE/live guns instead of unserviceable DP) that is the most(?) common cause of ZF in Brens
I guess in my mind, Peter, my more obtuse question here is since I am in the midst of a .308/7.62mm conversion to my Daimler MkII using a stock L34 BBL......is there any issue in milling off the horns on a spare std .303 bolt to match the L34 BBL face??
(I know that the .303 bolt is not "ideal" with the other issues of the larger bolt face as-is, but I'm not addressing that YET, just the fit of the bolt-to-BBL face.)
-TomH
You might try SARCO as they had some spare 7.92 Inglis bolts a while back. Get Dave on the phone and ask him.
My simple answer for the question was because it's a rimmed cartridge. OVERSIMPLE I admit. Looking forward to the details Captain Laidler Sir!
The .303 bolt is shorter so if you are doing a true conversion then it won't work. Also, an L34 is a silenced Stirling so I assume you mean a L4 barrel?
in what specific dimensions is the bolt shorter?? Do you mean depth of bolt face, or the whole bolt BODY is shorter. Not doing anything more than looking to make it successfully go 'bang' in .308.
Yeah, ummmm, I -KNOW- what a "L34" is......just brain farted when typing it. ;-)
-TomH
The overall length is longer than the .303, not much but enough that it won't fit and battery in a .303. Peter may be able to explain why, it may even link in with his question.
---------- Post added at 09:22 AM ---------- Previous post was at 09:20 AM ----------
Have you thought about the South African conversion? Probably an easier conversion for 7.62.
South African 7.62mm conversion........... Cheaper, but rubbish! We know now, following my total failure trying, that a home L4 type conversion CAN be successful
I guess I need to post up some pictures of the .308/7,62mm BBL I have here. It's not an "L4" BBL to be sure, but it is an arsenal/professionally-produced item. It's carrying a clone of the metric style "FN-FAL" flash hider-compensator from the "factory" so it looks weird. Any ideas/information as to origins is highly desired by me. SA origins...?? Then it could be an R1 clone muzzle device??
In some brief measurements though, it APPEARS to be made to fit with the std .303 bolt I am messing with.......anyway.......I'm me putting up some pictures FIRST before you go too deep into tearing me a new.......you know what.... ;-)
These images attached here are not mine originally, they are from a GB auction that I got it on. Looks NOS condition. I will have to get better images that show clearly the actual markings later tonight, so bear with me on those yet.
-TomH
POST ADDENDUM- Hmmm, guess I just answered my own query as to origins of this BBL!
South African 7.62mm Bren | Weapons OnLine
I don't know for sure but it LOOKS like a South African 7.62mm barrel from the flash eliminator. The breech end isn't compatible with a .303" breech block because it isn't recessed at the top of the breech face for the overhanging feed horns. The recess is for the extractor.
It's a South African barrel. I'm not sure they will even interchange in an Enfield L4 gun. Peter?? I helped deact a half dozen of the S/A conversions in '09 in Essex with Terry Abrams. I was intrigued by them but have to agree with Peter after finding a legit registered post sample here in the USA. There's no comparison.
By deepening the magazine well of the .303" guns to accommodate the smaller base rim diameter of the 7.62's has effectively taken the strength out of the magazine support *** feed lips in the body. Just as it did with the L4A1's. MUCH more to it than that of course.........
Hey guys.....let me back up and try to clarify things on my plans here a bit. First off, this is a plan for a 'hobbyist' shooter, I'm not too keenly interested in what an Military/National conversion plan was, or the depth to which such (well funded) entity came to a level of success or failure as a result of such attempt(s).
Where I am here, we burn ammo for fun, only. We shoot dirt and dynamite. Nobody shoots back, well, not intentionally at least. So we can tolerate a substantial amount of "non-standard engineering" results. Basic safety issues are the point of questioning, not so much reliability from a soldier's field expectations. Half of the MG's I am currently shooting were in the not so distant past a pile of torch cut pieces, so there is some tolerance built in to the game.
Now, my Bren is a factory original '42 Daimler MkII machine gun- still select-fire, never cut, never modified, so the amount of any future modifications I am willing to entertain is about nil. If I can hang it on the gun without cutting, milling, or drilling......it's a go, or at least I will give it a try. That said, "caliber conversions" for me in this sense is limited to what parts I can cobble together to make it run in any particular non-.303 chambering at a time. (Peter....I can see the look of abject horror on you from over here.)
If needed to reach a specific end result, I can torch, weld, cut, mill, drill, or otherwise manually or CNC machine anything I need to. This is just my first foray into Brit guns......I've spent most of my experience on other countries guns, so this Brit stuff is new to me, but not the basic education.
I am planning, after extensive due diligence following other people's reported results thereof on the various attempts, on using this SA 7,62mm BBL modified as needed to fir and function with an original .303 bolt, feeding 7,62/.308 cartridges through an unmodifed ZB-39 magazine, and not touching my guns' receiver at all, save for possibly the locking shoulder if needed. I am planning on "de-horning" the std .303 bolt so that milled flush with the front face of the bolt, it will mate up with the SA 7,62mm BBL face. Minus that, I will be cutting the rear face of said SA BBL to mimic the std .303 BBL face to accept the horns. Either way, LOTS of measuring and pre-planning to come before the cutting of either.
Will start with the currently installed locking shoulder, see where we are with that once the bolt face and BBL are mated. I can make a new one to any length needed, if needed.
Fit of the BBL itself is not an issue, I have lots of NOS BBL shims ( 2 sizes), and NOS Mk 3 BBL lock levers of several sizes (Nos. 1,2,3,5), and worse case I can turn down one for a custom fit.
I am not worried about getting a "correct" fit from these disparate parts as I can custom size any arrangement needed. I -DO- wish I could find original "Bren-specific" chambering gauges somewhere, though.......
The ZB-39 mags seem to hold a full 25rds of .308 ammo just fine, no problems so far. There is no need, zero, to do any serious surgery just to fit a "7,62mm magazine" to this project gun, the ZB mags run the 7,62 ammo well enough and they fit my particular gun perfectly, even using the std .303 mag latch.
Last issue, or maybe not, is the use of the std ejector......not worried.
-TomH
I believe the SA conversions used a modified .303 block by removing the horns and pressing/silver soldering an insert into the bolt face for the reduced diameter of the 7.62mm so you have no issues there. I have no idea about the ZB39 mags with 7.62mm but it's well worth a try, nothing to lose! What I do find unusual is that you say that the ZB39 mags will fit your Daimler Mk2, I seam to remember that none of my my ZB39 mags will fit any of my .303 Brens and I think this has been mentioned before and Kev G confirmed it. Could it be heavily worn?
Well, I am clueless on that point....all I can do is post up some pics showing my gun fitted with the ZB-39 mag, and fitting perfectly I might add, as a "drop in" fit. See below. I forgot to mention that my gun came with a very ersatz style of magazine catch, also pictured. All I can tell you is with THAT mag catch in place, ZB-39's snap in easily and are held perfectly in place, no wobble at all, just perfect. They slip right out too. I have no idea where that mag catch came from, so if anyone has any ideas, I'm all ears.Quote:
Originally Posted by Brit plumber
I am also re-posting a couple pics of the outside of the receiver to let you judge general "wear" of it?? It looks pretty "un-worn" to me!
-TomH
Your right, looks pretty good to me, I'll have to check mine again to be sure.
We've gone off track a bit here, which is a bit of a shame as it is an important safety related question......... But I'll bring it back into line! I know you've all been champing at the bit waiting for the answer to the Q. that I posed. It's one of those Q's bandied about during Apprentice Armourers training and on the advanced weapon designers courses. It's about the overhanging feed horns on the old Bren breech blocks. A couple of UK forumers have already commented that while it's an interesting Q., they're not in a position to find out because we/they have got chopped or angled off breech faces.
Anyway, here we go. In short, it is another mechanical safety feature. Unload your Bren and lay it across your lap, muzzle to the right and breech block to the rear. All hold your magazine in your right hand and show the empty chamber and magazine to me when I pass................. Oooooops...., sorry, just forgetting myself there - thinking that I was back in the classroom. Anyway!
Working parts forwards and put an empty magazine on the gun. Now, finger squeezing the trigger and bring the working parts fully rearwards and allow the working parts to move forwards under the load of the return spring(s).
The breech block will come to a STOP due to the feed horns coming up against the rear stop face of the magazine platform. THIS IS THE MECHANICAL SITUATION WHEN THE GUN WAS FIRING AND THE MAGAZINE IS NOW EMPTY. Now release the trigger as if to carry out the immediate action (commonly called 'the first IA') of COCK GUN, MAGAZINE OFF, NEW MAGAZINE ON............. As you are removing the magazine, listen VERY carefully to what is happening. As you remove the magazine, you will hear a very slight 'click' and although you won't see this, the breech block will move forwards by just less than 1mm.
This because when the magazine was empty the breech block was held to the rear by the extended feed horns on the mag platform. Remove the magazine and that obstruction is removed. Now the working parts, including the breech block of course will move very slightly forwards, just less than the 1mm I mentioned, and come to a stop again. THIS TIME HELD TO THE REAR BY THE SEAR.
When you replace the empty magazine with the new one, the feed horns will be AHEAD of the rear face of the magazine platform* but just behind the top round in the magazine, held back on the sear. All you have to do is to squeeze the trigger and the gun fires again from the open bolt until mag is empty again (or you release the trigger.
This holding open mechanism was a requirement of the UK Bren and caused a few problems for the designers at ZB. The longer cartridge and dimensional differences between the .303 and 7.92 guns, the only way they could incorporate the HOD and incorporate this as a safety feature was to extend the feed horns.
This feature - or LACK of this, or a similar feature came back to haunt the L4A2 variants of the gun later........... With several fatal consequences. But that's another story
*if you put an empty one back of course
Peter....that's interesting. I'd would love to see the communications that went back and forth during the negotiations with CZ!
I have seen this EXACT sequence of mechanical events described in other guns, however, as a designed in means to alleviate extended wear on the face hardened surfaces of the sear itself, albeit, at the expense of wear on the much cheaper and easy to replace (throw away) magazine follower. Stopping hard every time on the sear face would invoke the kind of wear that would possibly require a replacement of either the sear itself, or the bolt, but heavier mass almost always wins in those kinds of arguments, so what I have seen discussed in guns like the BAR is that nobody wanted to try and pull apart the trigger group to replace the sear if it snapped off at the nose, so the bolt bent was left un-hardened as the sliding out the bolt was easier then unpinning the relatively complicated trigger group parts, and even before THAT contact was allowed to happen the magazine follower became the sacrificial part in terms of wear.
There is also such a safety design incorporated into many such guns with heavy bolts, the US M3/M3A1 SMG's for example instead have the sear devoid of face hardening, whereas the bolt bent is (flame)hardened instead, the sear being adjudged cheaper and easier to replace if burred or broken.
Either direction used, there is often the intention of making one part "sacrificial" in materials design to prevent undesired wear on the opposing mechanically interacting part.
-TomH
I have to admit I'm still a little confused, I understand how the feed horns hold back the block against the hold open device on the mag platform, and this is before the bent on the carrier engages with the sear, but I'm not sure why the feed horns over hang the face of the block. If it's just to get the clearance between the HOD and sear, why not use the standard length block like the 7.92mm as the geometry at the rear of the gun (Position of sear, locking shoulder, rear of magazine etc) is the same for the 7.92mm and .303" guns. I can only think that due to the .303 being shorter than the 7.92mm, that the breech of the barrel needed to be further into the body of the gun so that the round when fed from magazine to breech, had less distance to travel unsupported. I can't check on this as I can't get in the loft at the moment.
BP. It's simple if I understand your confusion........ If the feed horns didn't overhang, as soon as you took the magazine off, the breech block would go forwards and dry fire. Which isn't what you want with a HOD! You want it to HOLD OPEN. Now, you remove the magazine, breech block goes forward 1mm now to be held back on the sear. Loaded magazine on and squeeze the trigger and carry on firing!
The problem faced by some MG's as described by Tact (thread 23) don't apply to the Bren because the distance between the piston extension at it's rearmost (at the buffer face until it moves forwards to be engaged by the sear is minimal. And during this minimal distance/movement the heavy piston extension and breech block assembly have not gained sufficient momentum to cause damage to the sear bent in the piston post or the sear face.
BUT this WAS a problem with later modified L4 guns that had a secondary sear bent machined into the piston extension. See last para thread 22!
Tom,Quote:
Originally Posted by TactAdv
Wally G posted this awhile back about caliber conversions:
Caliber conversion on BREN? to 7.92 Mauser or 7.62x51 NATO?
Both Wally & I only have semi auto Brens, so FA may have other issues. I've also been fooling around with caliber conversions. Below is a pic of a 7.62 Nato round in the SA Bren barrel. You can see why no mods are necessary to the barrel using a regular Bren bolt. Wally has fired his conversion as noted in the above post. I have to make semi auto denials cuts on a .303 Bren bolt I have to try it with an unmodified .303 bolt and L4 extractor. Interestingly I have a .303 bolt in my MkII that has been modified for 7.62x54r and has the standard .303 extractor. It headspaces properly with the 7.62 Nato round. Also it will cycle and extract the 7.62 Nato round using either a ZB30 8mm mag or the ZB39 mag. I also have an .303 Bren barrel that was re-chambered and re-bored for 8mm Mauser. It also headspaces, cycles and extracts with the 7.62R bolt and standard extractor.
When I had the 8mm work done I had the back face of the 8mm located at the same plane as the rear of the .303 so it would headspace with bren bolt with no adjustments.
The ZB39 mags were too loose in my Brens so I had to add a shim in the front. C310pilot used one of my zb39 mag I had converted to 25 rd 7.62x54r and found they would not fit a zb39 receiver, they fit fine without the shim.
I found to use the zb39 mags for 7.62nato I had to remove the box guide on the inside and grind down the horns on the rear of the follower about .040" or the last round would jam or not feed. You can also modify the bren receiver to accept the zb30 mags which will feed the 8mm Mauser or 7.62Nato.
Joe
Attachment 59381
Quote:
When you replace the empty magazine with the new one, the feed horns will be AHEAD of the rear face of the magazine platform* but just behind the top round in the magazine, held back on the sear.
Thank you, Peter.
It’s interesting to know how it works, not just how to operate it.
I understand how and why the hold open device works with the horns but what confuses me is, why not make the block longer like the 7.92mm block (Thus not requiring the overhanging horns), that works fine as the geometry at the rear is exactly the same as the .303. The only reason I can think of for making the block shorter and therefor requiring the over hanging feedhorns (bringing the feed horns back to the same length as the 7.92mm block) is because of the .303 cartridge being shorter than the 7.92mm and therefor the barrel needs to sit into the body slightly further than the 7.92mm or else the .303 round has no support between being pushed out of the mag lips and entering the breech of the barrelQuote:
Originally Posted by Peter Laidler
Thanks Peter! While I was well aware how the hold-open worked, I never realised that was the sole reason for the extended feed horns. It all makes sense when you think about it!
Ah, see what you're on about BP. But the fact is, the gun is what it is and wot they designed is wot we got inn'i! A lot of the reports made comment on the fact that the new ammunition (I suppose they meant 'new' in relation to the gun that was on trial) was shorter than the original configuration of the gun was designed for and further geometric designs were out of the question. This was because every design change cost thousands of £££££'s in extra licensing agreements. That's why we retained the absolutely ridiculous zillion TPI and threads on an equally ludicrous threads on a ludicrous diameter farce.....
This shortening the cartridge yet again for the 7.62mm L4 guns caused even more headaches including a what is called in weapon feed systems 'a twilight zone'. That is just a tiny fraction of time or distance where a round being fed is uncontrolled. This is a great taboo and however short the space, distance or time and however long and detailed the trials, if there is even a slight sniff of a twilight zone, the gun WILL jamb and/or misfeed EVENTUALLY. And anyone who's been on active service will tell you, it does this when you really don't want it!
Incidentally, the original trials X10 guns (the earliest 7.62mm guns) the breech block came to a rest/hold-open against the rear of the empty magazine platform. But due to the inertia imparted to the heavy breech block and piston assembly by the return springs and distance travelled from the buffer face to the rear face of the mag platfrom, the platforms were buckling under the imparted inertial weight. That's why they had to come up with a better idea of a mechanical HOD. I say better but an actual HOD as opposed to a magazine stop mech is notoriously fickle. Shall I go on a bit..............
The L4A1 HOD atually wasn't too bad but..... The GOOD bit was that although the user handbook forbade it, it was simple to override! It was THIS that lead to a complete re-think for the A2 onwards guns. And its this............ The Small Arms School (actually W02 and later Major Maurice Fogwell had already questioned the need for a HOD at all because the actuial drills, drummed into everyone from his first LMG lessons was the first immediate action (the first IA). And that was this:
GUN IS FIRING OK. GUN STOPS FIRING. COCK GUN, MAGAZINE OFF, NEW MAGAZINE ON, CARRY ON FIRING.........'
So he rightly stated in the user and technical part of his trial report that there was no need for a complicated HOD device because the first part of a stoppage (and it's easy to forget that an empty magazine IS a stoppage.....) was COCK GUN. So the HOD was already redundant and deleted from any further mark/types of the gun.
I would imagine an experienced LMG operator would have had a fair idea that it was an empty mag that caused his stoppage after 10 bursts of 3 rounds. Do you miss the Job now your a Mr?
On a rundown during a Bren pairs shooting comp when you've been practicing for weeks you've probably got the hang of 3 round bursts but in Korea or Malaya or wherever, it might be a tad different! Nope, don't miss it a bit to be honest. The bit I do miss is not just being able to walk over to the technical or workshop stores for 'stuff that you need'