54R Bren Issues

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Originally Posted by Vincent

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.

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IMO 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.
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

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Originally Posted by Bruce_in_Oz

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.

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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.

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 ----------

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Originally Posted by Joe H

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

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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

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Originally Posted by TactAdv

a well worn 7,62x54R reamer

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Would make the reamer produce a smaller than standard chamber, not bigger.

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Originally Posted by browningautorifle

Would make the reamer produce a smaller than standard chamber, not bigger.

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But not in the correct proportions. It is the mismatch in chamber shapes that is causing the lack of adhesion.

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

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Originally Posted by TactAdv

'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.
Just a data point for you.

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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.

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