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It’s a tube gun with a modern sound suppressor that makes it extremely quiet. The finish is powder coat. There are a few things left to do, but I thought some of you would enjoy seeing it.
Of course we do. You know I'm up for this...wondering how much the suppressor is varied from the original design, J baffles? K baffles? A far cry from the Archimedean screw... You should do a short vid when at the range next...? Both with subsonic 147s and with 115 ball. Just for yuks...
Is the breech block eccentrically machined internally too? We didn't like the wood hand grip for some reason. Probably cheapness. Is the barrel the standard un-drilled version. Interested to see how they improved on the silencing properties. I wish I had access to the MPL high speed video of the trials. VERY interesting design aspects were highlighted in it
It has an M stack in it at the moment. I am going to replace them with an Omega stack or a monolithic if I can get the FRP down enough.
It doesn’t have the long rods but the layout is basically the same as the original, ported barrel, baffles and expansion chamber.
Attachment 65579Quote:
Is the breech block eccentrically machined internally too?
Yes, it is.
The blue heat mark is where the metal is very thin and couldn’t dissipate the heat from cutting very well. There would be a hole on the left side if was machined symmetrically. Patchett knew what he was doing when he offset the hole to the right.
Attachment 65580
The barrel is drilled. Real Mk5 barrels are not to be found here. I will fill a barrel with melted lead and drill the holes in rifling groves and melt the lead out when it gets cooler here.
I know that's the theory and all...but I found it didn't make a whale of a difference...Quote:
Originally Posted by Vincent
Maybe it keeps the bullets from shaving a bit though.
Theres more to it than that though BAR. It's all to do with the mathematics of the gas loss, boyles law and all that stuff and integral strength that the drilled barrel retains.
The total area removed by the holes was just slightly more than was mathematically required to gradually bleed off just sufficient gas as the bullet was traveling up the bore so that the m/v would never quite reach the speed of sound. And don't forget that as it is traveling up the bore, initially, the propellant gas is still being produced and that has to be dissipated too.. It was calculated using NATO standard Mk2z ball ammo.
They were drilled radially because if they were drilled in a straight line, in say 4x rows, the distance between hole centres would be so close that it could/would affect the structural strength of the barrel. By following the rifling the holes are offset to each other and structural strength of the tube remains sufficient to withstand proof.
If you fire a 9mm UK Military proof round in a barrel with 4x linear lines of holes the barrels will stretch and bulge*. But not with the holes radially drilled
* I cannot confirm this as I am repeating what I was told and read in the trials stuff
Just been reading this again and it doesn't seem to read right!........... But it's getting late as well! Later I'll mention the brilliant design of the muzzle cap.
I think all this is what I read before...encapsulated. I suppose the ones I've dealt with haven't undergone the rigors of military testing and will never see much use...don't know how I'd manage to do them in the grooves...?
What’s available here at a reasonable price is off the shelf pistol FMJ’s, 115gr and 124gr. To get Mk2z performance you have to go to a +P and they are usually JHP’s that don’t always feed well in a Sterling. You can buy ball with Mk2z performance, but it’s very expensive. So the barrel in the picture is optimized for what’s available here at reasonable prices, pistol ammo that’s about 110 ft/s slower than Mk2z. Instead of 72 holes the barrel only has 69 holes.
The pistol ammo puts less strain on the barrel and when you’re dumping gas to keep the muzzle velocity down there’s no advantage from higher performance ammo. It just makes more gas that has to be vented to keep the bullet subsonic.
I don’t know how the barrel would take a squib load. I have had them with the Mk4 and they bulged the barrel, but the gun kept running.
I am looking forward to reading that.Quote:
Later I'll mention the brilliant design of the muzzle cap.
“Simple” or “Plain” indexing with a dividing head is one way.Quote:
don't know how I'd manage to do them in the grooves...?
I'd still probably use 147 subsonic factory. Shouldn't break the bank for bulk buy.
Can you recommend a brand of 147?
I have tried a few brands in pistols. They seemed to have a lot of blow back gas and need a booster to cycle reliably. I am not sure they would push the Sterling breech block back far enough.
Fiocchi and IMI 158gr seem to have less blow back gas and work without a booster. I wouldn’t think 11gr would make much of a difference. Maybe it’s the powder?
Attachment 65628
The back half screws onto the barrel just like a pistol suppressor. The front half screws onto the tube. It’s very light.
I think that this has been mentioned here but did Canada have any L34 guns BAR? SF or the like? I ask because in the register were sales '....with gaps' and some large noticeable gaps!. Obviously these were sales via the UK MoD or Govt on a restricted Govt-to-Govt procurement basis where sales were logged in and out of course but further than that everything else was restricted. Not that it affected the book or any research but just out of interest it whetted my appetite............ Incidentally, there were no non-serial numbered guns that people who-need-to-get-out-a-bit-more speak of.
There would have been some trial guns for sure, and someone mentioned that as confirmation. I never did see any nor did I know anyone that had. Too bad, I had one come past me a few years back and they're do-able...we should have had a small quantity... We didn't really have an "SF" until JTF surfaced and the Airborne was just that. They had mostly standard stuff. Mostly...Quote:
Originally Posted by Peter Laidler
And how about that brilliant design of the muzzle cap..... inquiring minds want to know. :D
The design drawing of the muzzle cap is in the Technical Manual.
Attachment 66082
:confused: Is this it?
I think so. Did you reference the L34A1 Technical Handbook?
I don’t have a copy.
My mistake Vincent. I thought I sent you a whole set of Sterling L2A3/L34A1 literature several months ago. I still have them available if interested. As I've said many times before; I can't imagine doing these builds without the EMERs, technical handbooks, illustrated parts catalogues and even the user handbooks in the reference library.
Oh! How that you mention it, I think you were going to send them along with another item. I am sorry. I completely forgot about them. I apologize.
Ah, yes, the muzzle cap. Remember that what follows is not a scientific paper or a classroom lesson. Ideally the subject would be discussed with the aid of the National Physics Lab high speed video and the component parts of the silencer unit spread out on the desk in front of you..........
The gun has just fired a single shot and the bullet has just left the confines of the spiral diffuser. As the gas enters the front plenum chamber (the gathering chamber shown in thread 15 above. Item 31 P179 in TGOD)) from the foresight mount block (TGOD; 36) and spiral diffuser (TGOD; 1), the gas enters the plenum chamber. It spreads out radially at 29 degrees and some of this now waste gas that we're desperate to get rid of overtakes the heavier bullet. As it does it meets with the specially shaped internal compound curvature of the muzzle cap (TGOD; 28). a very small amount of the gas that has passed the bullet will naturally emerge from the muzzle. A millisecond later, the bullet passes through the muzzle hole effectively sealing it. Remember this later........
Simultaneously, the waste gas remaining inside the silencer is directed by the internal shape of the muzzle cap to form a high pressure point centrally and directly behind the muzzle opening. This high pressure wave very effectively closes off the muzzle opening behind the projectile, sealing the unit and trapping the most part of the waste gas inside the front plenum chamber. Only then, a millisecond or so later the pressurised gas INSIDE the chamber neutralises/equates itself and as it attempts to revert to atmospheric pressure it simply takes the line of least resistance and vents to the outside atmospheric pressure and exits the muzzle as a puff of smoke.
So if you are looking at the slow motion video from the side, this what you'll see. First, there's the first feint puff of smoke followed by the bullet on its way silently to the unfortunate target at just below the speed of sound. Then - nothing..... but.......! Followed a short time/milliseconds later as the internal gas vents slowly and silently to atmosphere.
It's all down to the internal inswept design of the muzzle cap and the mathematically calculated area of the plenum chamber. There is absolutely no doubt in my mind that the arch genius George Patchett dreamed up this feature but that the NPL perfected it for him. There was a second design on offer by Sterling shown elsewhere in the book that eliminated the plenum chamber or extension tube (TGOD; 31) whereby the muzzle cap sat on top of the plenum chamber via a .75" or so long tubular ring that replaced the extension. But there were few, if any, takers. George Patchett had heard my oft repeated words. If it ain't broke, then don't fix it.........
If you liked or appreciated this short explanation, please tick the thanks box..........
I always like a good technical description...
Thank you for that great technical description, Peter. I looked for the high speed camera video on the NPL website. http://www.npl.co.uk/publications/videos/ They have some interesting videos. I couldn’t find the silencer one.
I did find this one on youtube that shows the expanding gas and the bullet traveling through a suppressor.
https://www.youtube.com/watch?v=fPqa3teOQkA
There’s some slow motion in this video of a Mk5 where you can see those smoke puffs coming out of the suppressor.
https://www.youtube.com/watch?v=ZRLcEHD2K5E
Unfortunately I can't see the video's you are referring to Vince. The atmospherics of the L43/Mk5 were truly emphasised on the video especially when the great Lt Col Mike Txxxxx was doing the teaching. It all made sense on the range later. I wish I remembered the saying we used about silencing weapons. Went something like '..... add different quantities of A level mathematics with some A level physics with some thing else........... Anyway.........
Glad you all liked the schoolboy explanation!
Incidentally, if yoiu do have an original Mk5/L34, the inside of the muzzle cap and front end of the extended tube do get a bit of a pasting so it's worth machining an exact copy from stainless and use that if you want the gun to last the course
To be quite honest Peter, what I found with suppressors was there's a number of principles and factors that are involved...and as long as you don't violate any of them too badly things seem to work reasonably well...I never sat in class for any of it and physics facts escape me...mostly. That is until a student one day announced to me I was teaching physics in rifle class...:dancingbanana:
The difference between 147gr and 115gr is noticeable.Quote:
Originally Posted by browningautorifle
I am still working on getting this gun dialed in. The Israeli 158gr is fantastic!!! It’s the quietist 158gr I have tried so far and it’s reliable. Some of the commercial 158gr and 147gr have trouble getting the breach block far enough back to engage the sear.
All the brands of 124gr I have tried so far have been 100% reliable and quiet enough not to disturb the neighbors. (There’s no need to take this one to the range. It’s “backyard quiet.”)
115gr makes some noise. It seems to be from the breech and there was more gas blow back. It could also be the powder as I have only tried two brands. I have several options to add more mass to breech block, starting with the block, cocking, handle. If that’s not sufficient, there’s an unmodified breech block and/or a firing pin retainer from a Mk6 semi-auto. So there are several combinations to try. A stronger return spring is also an option.
I have a Chilean FAMAE PAF breech block that’s very light. We will see how it does with the 158 & 147’s.
Maybe I can get one of the kids to help me with a video after I have the gun sorted.
Speaking of A level math, I find the formulas in The Machine Gun by George M. Chinn very useful. They are handy for calculating things like breech block weights, throw and spring rates for blowback guns. I normally use them in a program that lets me adjust barrel length, bullet weight, powder charge, breech block weight, spring rate and pretention so the cartridge case is where I want it when the bullet leaves the barrel and the pressure drops. It works great with a normal barrel. But the Mk5 doesn’t have a normal barrel. The pressure starts dropping before the bullet leaves the barrel. So field testing is my only option. It’s not really a burden. I actually like being able to shoot in my garden and not be heard. And those garden gnomes are irresistible targets.
Well, it IS physics isn't it?Quote:
Originally Posted by browningautorifle
Newton would be proud.
My junior grade school math teachers would have been stunned...Quote:
Originally Posted by Paul S.
Attachment 66352
Chrono arrived in time for some testing tomorrow.
I need to know the speed of the different weight bullets as they leave the barrel. Then I can calculate breech bloc weights and spring rates for each.
I will try the same ammo with my Mk4 to see how much the Mk5 barrel vents slow the bullets.
Also, I have always wanted to know if the long Mk6 barrel makes the bullets exit at a higher speed.
And we'll see the results here later for consumption...?
Absolutely.
I wonder how a long barreled Mk6 would function using a blowback/API L2A3/Mk4?
That’s an interesting question, Peter.
Doubling the barrel length would require a considerably heavier breech block.
The Mk6 barrel has a deeper chamber than the Mk4 barrel. Would it still have API in an open bolt system?
I don’t understand how API works with a fixed firing pin on the breech block. I know it does work because I can see and feel it. But how is the primer ignited while the round is still traveling forward?
I understand how API works in the long chambered Oerlikon cannon. But I have never seen an explanation of how it works with a fixed firing pin.
I still think that's just theory. I think the cartridge has actually stopped and the breechblock is still moving, that I'll buy. I know, I've taught the classes on the Sub Machine Gun C1, mechanism...still...
So the firing pin protrusion ignites the cartridge and in a fraction of a second the cartridge case starts to move back while the breech block is still moving forward?
I wrote an article about API on the forum and basically it's as BAR has said but API as a stand alone feature is not of itself special. It is simply an incidental feature of having a fixed firing pin. Maybe someone wot is comu'a literate can bring the article up. Anyone........?
The primer's ignition depends on the firing pin protrusion and the hardness of the primer. The cartridge firing cushions the bolt's forward movement which is the most important feature, I still don't like slamming those heavy breech blocks against the breech faces dry. Yes, the theory is the bolt is still moving forward when the cartridge goes off...but if the cartridge is too, then why do we get out of battery firing early when you have a gritty chamber. The cartridge is in fact as far forward as it is going when it fires, no matter what. It's not still going forward. That's a theory on paper.