54R Bren Issues

[ActionYobbo]

its a dangerous practice to shoot ammo thats has the case lubed. the case is suppose to adhere to the chamber walls while under pressure. lubing cases will put the entire load on the bolt and its locking surfaces

[djandj]

its a dangerous practice to shoot ammo thats has the case lubed. the case is suppose to adhere to the chamber walls while under pressure. lubing cases will put the entire load on the bolt and its locking surfaces

NOW you tell me Mr.E! (lol) fortunately, it didn't seem to make any difference either way. I don't seem to need to lube them now anyway

[tankhunter]

Military Proofing is: One dry, One wet (Oiled) Rounds. Lubing the case DOUBLES the Breech Pressure!!!...............

I am Still of the opinion that this is a Headspacing issue! Get the headspacing Correct, (0.64"-0.74") & THEN try a couple of rounds. It
SOUNDS like the H/Spacing is Insufficient to Me!.....

[Peter Laidler]

At last...... DJ, now we know that the only problem remaining is that the lubed cases* show us that the chamber walls are imperfect and the lubed cases will not adhere to the minor imperfections. All you need now is a correctly chambered 7.62x54R barrel and you're good to go.

I disagree with Tankie about the CHS for a different reason to his common sense and obvious theory. Because CHS won't cause cases to blow out and we know that lubed cases WILL eject manually. .303" bren cases will also eject manually, easily too because of the perfect P-E inbuilt into the unlocking of the breech block. We had a couple of gas regulators with welded up gas holes that we used when just zeroing new barrels to guns. This was because we KNEW the guns worked so we used a solid regulator so that the gas parts stayed clean. No cleaning of dirty gas parts after zeroing gun! Simple! You must have seen those gas regs hanging on the range bay at Warminster Tankie!

*appreciate what you're saying Mr E but lubing in this case was just for the purposes of eliminating the sticking case problem - which it has!

[Joe H]

Djandj,

I'm glad you are satisfied. Hate to be a 'wet blanket" but as I said in my first post on page 1 of this thread

"After one blow out, another should never have been fired until the problem was solved."

I have to agree with Tankhunter and others that it may be a headspace problem. Not too much if your measurements are correct but maybe too little causing problems with the bolt closing.

I'm not offering conjecture. In the pics below you can see a typical blown 54r case. Notice the separation occurs .130" below the rim base. The other pic shows a Bren .303 barrel. The notch is .100" below the face of the barrel.

For this case to separate (blow) the base of the rim had to be .030" (.130-.100) off the head of the barrel and under pressure. This is more than double the allowable "Field" headspace .074-.062 = .012

For whatever reason the bolt is not properly locked or is unlocking prematurely. Find out what is causing this problem and your Bren will run on all ammo.

My 2 cents

Joe

[djandj]

Djandj,

I'm glad you are satisfied. Hate to be a 'wet blanket" but as I said in my first post on page 1 of this thread

"After one blow out, another should never have been fired until the problem was solved."

I have to agree with Tankhunter and others that it may be a headspace problem. Not too much if your measurements are correct but maybe too little causing problems with the bolt closing.

I'm not offering conjecture. In the pics below you can see a typical blown 54r case. Notice the separation occurs .130" below the rim base. The other pic shows a Bren .303 barrel. The notch is .100" below the face of the barrel.

For this case to separate (blow) the base of the rim had to be .030" (.130-.100) off the head of the barrel and under pressure. This is more than double the allowable "Field" headspace .074-.062 = .012

For whatever reason the bolt is not properly locked or is unlocking prematurely. Find out what is causing this problem and your Bren will run on all ammo.

My 2 cents

Joe

Right with you Joe! Head spacing is the next thing to try. I will get Vince's shoulder piece and take a feeler gauge measurement. Try both brass and steel and report back.

[tankhunter]

As I said. If you start from a BASIC & VITAL standard. IE: Headspacing, then you should in theory, be in with a chance of the gun operating properly. It is very difficult for us to say for definite, any problems for sure. without actually having Hands on the subject weapon.
But ONLY from what I have observed here, & what has been stated. As to the main problem of the case blowing. I can only offer my Opinion that it would APPEAR that this particular Gun's H/Spacing is insufficient If this is the case, then it is NOT correctly locked up when firing. & the pressure generated combined, WILL indeed cause this problem. Also, It hasn't been explained, if any/ one of the return springs has been cut down/ Omitted either. To overcome the Differing pressure of the STRIKER Block Operating spring. This will also have a bearing (Albiet small) on unlocking/ timing I feel.
Just another thought that MIGHT be relevant? Have you carefully checked the chamber at all? It should be highly polished to aid extraction. If there is any light pitting Or a rough surface from not being PROPERLY Cleaned at all? These factors need attention if that is the case. They generally cause hard extraction, & it's easily overcome with polishing the chamber. But This problem of the cases blowing, is I feel Headspacing being too tight. Peter will have his Own theory of course. with His College Graduites head on. He will more than likely be able to tell you the batch number of the metal that the barrel was manufactured from!..... We are both well versed on the Bren & LMG. But the trouble is. we have never seen a Semi-Bren in the UK. & the design (Some ingenious!) alterations to enable ownership legally in the US. Differ Immensely from an 'Original' Bren in so many ways. That without a Proper 'Armourer, hand's on Approach'. We Cannot say for Definate what the problem is! We can only apply our 'Expertise' from knowledge gleaned on this weapon System. from a Service Viewpoint. Which after all, was where the 'Semi' Bren's emerged from!...........

Hi Pete, yep I saw those gas plugs during my time at Warminster. Plus a few other 'interesting' articles lying about!.......

[Peter Laidler]

I see the point you're making Joe regarding the depth of the recess for the extractor that is allowing the steel case to blow out. But this greater depth you illustrate is caused by the old .303" chamber being reamered out at that diameter from .453" to .491" (I'm just using a few old fired cases here so nothing too accurate.....) to accommodate the 762x54 cartridge. In my humble opinion, it is this additional machining of the tapered chamber that is nibbling away at the external taper of the externally tapered extractor way that is causing this .030" difference and not CHS.

[Joe H]

I see the point you're making Joe regarding the depth of the recess for the extractor that is allowing the steel case to blow out. But this greater depth you illustrate is caused by the old .303" chamber being reamered out at that diameter from .453" to .491" (I'm just using a few old fired cases here so nothing too accurate.....) to accommodate the 762x54 cartridge. In my humble opinion, it is this additional machining of the tapered chamber that is nibbling away at the external taper of the externally tapered extractor way that is causing this .030" difference and not CHS.

Peter,

Excellent point. I do have a 54r barrel that has been reamed from a .303 barrel and the depth of the notch is .100" (same as the .303)

I've attached one of Dandj's pics of his blown case. Blow it up a little and put a scale on the blown case and measure from under the lip to the blow out line. Use the scaled distance on the barrel. The blow out line will be significantly below the notch on the barrel in the pic. I scaled that the blow out line was 1.23 times the depth of the notch. If the notch depth is in the .100 range the the blow out is 1.23 x 1. = .125". Field HS is in the 12% range so using Djandj's pic we are double allowable HS. Not exactly precise but we should be in the ball park.

I've also posted two other previously posted pics showing results of the oversize .303 Bren chambers and my 7.62 x 54r barrel that shot the blown case. The blown case happened when I was trying to correct drag problems causing the carrier and bolt not to close properly. I didn't even know it happened but I found it in a pile of cases I had from my initial set ups. Never had a problem since and any current spent cases go in the trash can at the range.

The difference in the theoretical case diameters is .4598"- .487" = .0272 ". Since the Bren is oversized by at least .010" the difference becomes .0272-.010 = .0172" Now only 1/2 the diameter difference would affect the notch .0086" If the slope is 45 deg the depth diff could be .0086" , not enough to solve the issue.

Joe

[Peter Laidler]

Give us Brits a bit of slack Joe as we (me and Tankie) are talking blind here. As he says, we're just bit part amateurs here when it comes to the semi autos!