OOB premature discharge question

Has anyone experienced a Bren having an out-of-battery premature discharge ??


I was working with a chap recently on a television show in where a Bren was being used, however I was not on set when this problem occurred. According to the armorer who was there, the primer of one of the rounds (it was older 1950's ammo) had been completely blown out of the primer pocket , and had gone off prematurely and caused the remaining rounds in the magazine to blow out through the bottom of the floorplate along with the spring and magazine follower.

Correct me if I'm mistaken here but doesn't the Bren's bolt design prevent it from firing if it's not in battery ??

I suspected that it may be something more than what was indicated.

Nobody was hurt when this happened , and both the set armorer and the gun rental company armorer have checked the gun and have declared it safe.

I'm just curious if it may be something with the ammo.

Thanks

Gary

I dont see how this could ever happen, the firing pin will not protrude through to the bolt face untill the bolt is locked and the carrier moves forward to lock the the bolt against the locking shoulder. Also, how did it set the other rounds off? The round dosn't sit into the breech face untill its cleared the magazine. The only thing that I can think of is that the first round was some how jammed incorrectly in the mag and one of the feed horns contacted the primer and initiated it. Thats a slim chance though!

How random.

Firstly, I'd question the set 'armourer' (no capital letter here note.....). Many people have been known to call themselves Armourers, including those living in TV and Cinema land. The less said about them, the better...........

In theory, what BP said above is absolutely correct. The mechanical safety features built in the gun ensure that it CANNOT fire until the breech block is positively locked behind the locking shoulder AND it has travelled a further .25" or so further forward. Thus making doubly sure that the breech is locked.

HOWEVER, if your 'armourer' (note, no capital letter here) hadn't ensured that the barrel nut was locked down, then at the moment of firing, the barrel could tend to move forwards a tad and the cartridge case is still gripped by the tightened extractor claw so it will fire. At the instant of firing, the barrel will try to move forwards a bit more and if it's not locked, then it certainly WILL move. Not a lot, but sufficient to allow a lot of expanding gas to enter the body, bulge it (yes it will.........) and seek the least line of resistance. And that is usually out of the top of the magazine.

AS for checking the gun afterwards and declaring it safe............. I dispair.............. Film and TV armourers........ and those 'police' armourers - we've seen 'em all before! Enthusiastic, yes, amateurs, yes, enthusiastic amateurs, definately. But Armourers..................

Peter, With regards to your comments concerning TV set 'armourers'? (Sic) You put it a damm site more politely than I would! I have been known for my position on intolerence towards these 'sort of people'! I think you could say it like, 'They were left in ABSOULTELY No doubt as to my thoughts as what they THOUGHT they were!!! As for police 'armourers', (Unless they are EX S.E.ME. or Carlisle Etc Establisment trained) well, I wouldnt trust half of them with a Waterpistol!!!!!!!!!!! Rant over, may I get my coat now please?......................

Peter and company,

Thanks for the replies on this subject. You confirmed what I had first thought that it's not possible to go off like that.

Would a pierced primer do similar damage ?

Just to clarify, the remainder of the rounds in the magazine did NOT detonate, but the OOB discharge caused the remaining rounds to exit the magazine through the floorplate and land in front of the gun.

My suspicion is pointing to the ammunition. Old 1950's rubbish which is known for hangfires and slow ignition.

The set armorer in question is a US Army veteran armorer, who is a pretty decent bloke with guns, if anything can be said his only fault is lack of knowledge on older British Weapons (which is why they asked me to come out, unfortunately after the fact)

The studio services that rent the weapons are utterly clueless. They butcher and bastardize weapons to make them serviceable to fire mostly blanks, so when it's really needed to fire live rounds, they don't necessarily work 100% reliably.

Don't get me started to what they did to the poor Vickers Gun in this weeks shoot............

Agh, I get you now, when you said blow out, I thought the 1st round had caused some of the rounds in the mag to go too.

What did they do to the Vickers gun? I would expect that to be a pretty easy conversion to blank fire.

Effendi:
On the Congo border in the 60's there was an AD (accidental discharge) resulting in a fatality. According to the Bren gunner who had finished cleaning the LMG the working parts were back and the body yet to be rejoined. The gunner than placed a full mag onto the body and slammed the working parts and body together in order to push home the body locking pin. Upon slamming the parts together the Bren fired a single fatal into the RLI Pte seated a few feet away.
There were many attempts in the following days to replicate conditions but could not get a similar 'slam-fire' --- the offending troopie was rearward bound regardless.
20 years later a highly esteemed member of the REME encountered a similar AD - a slam-fire with a 303 cal Bren. It just did not make sense to the Enquiry -- however a real Armourer noticed high primer seating and said so in his report.
regds from the colonial side
roconn

Roconn

My thought was that a primer that was possibly punctured and got stick to the firing pin which may have contacted the primer of the next round causing the OOB discharge.

Brit Plumber,

They "converted" this poor old Vickers into an "aircooled" gun, by drilling two holes in the front of the water jacket !!
I'm sure fro blank fire it was fine, but when they attempted to use it for live fire the vibration and occillation of the gun made hitting the target impossible. It also casued so much vibration ,the booster cone would work loose after every 100 rounds and start to fall off !!!

If the 7 pints of water that should have been in the water jacket were in place the vibration and occilation would have been dampened down to almost nothing.

These studio guns are a nightmare.

I need to get a Vickers MMG to rent out !!

Gary

were hangfires noted before the discharge?
was the gas regulator on the highest setting, to compensate for perceived short recoil, with previous firings from that batch?
was there anything unusual reported with the other primers (piled metal)?

Quote:

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Originally Posted by mrspeel

were hangfires noted before the discharge?
was the gas regulator on the highest setting, to compensate for perceived short recoil, with previous firings from that batch?
was there anything unusual reported with the other primers (piled metal)?

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Yes to all of the above , the gas was on #3 when I saw the gun.

Someones pointed out to me that if the gun had the ORIGINAL Mk1 type barrel nut, then it wouldn't have happened because that nut had a block to prevent for and aft movement of the piston extension if the nut were raised. But this block was removed during the first simplifications to the gun in 1939/40. On the basis that '.....with the proper and correct training, such an event (leaving the barrel nut undone) or using the gun without the barrel nut fitted never likely to occur'. The wise old trials engineers of 1940 didn't cater for enthusiastic amateurs though.....................

Back in the day, when it was legal to shoot the Bren in Canada, as a converted auto (ie semi only), I experienced a couple of issues with surplus ammo in an Inglis Mk1m. It was '5o's era 'GB' mk 7 ball, on stripper clips, in slings, pulled straight out of the case. While the ammo appeared bright and clean, it produced hang fires and short recoil/feeding failures. After I retrieved my cases, I noticed that the bren firing pin "indent"was now an "outdent". The metal was "standing proud" on the firing pin, like a square triangle.

What could be the cause? Primer, powder?

To quote Major LM Yearsley, from a UK May 1990 Guns Review article" if the firing pin can bounce, so can other moving parts of a weapon mechanism. This applies to the piston of the gas operated machine gun. This, in combination with hang fires, can produce a pattern of behavior which can lead to the user drawing quite misleading conclusions as to the cause."

The Major goes on to write that "In the early sixties, a complaint of weak ammunition was received from the Middle East, in connection with the .303 bren. Short recoil, due to insufficient gas, was suggested by both the user and the local investigator, as correct functioning proved to be impossible, even with the gas regulator set to its larger hole.The gun and a sufficient sample of the ammunition date of work in use, were sent home for investigation."

The Major reports that the reproof confirmed the ammunitions working pressure was within specification. The fired cases, both those returned, and those collected, showed "very severe piled metal, the deep impression of the bren firing pin standing, in many cases, almost as proud of the cap surface as it had originally indented".

The hang fires, piled metal, and short recoil, were explained by the following theory: "in effect, each cap had fired at the protrusion of the firing pin, but the duration of the hang fire was such that the bounce of the piston had permitted almost full withdrawal of the firing pin before the rise of internal pressure, which was normal, had forced the indentation in the cap back into contact with it. by the time the gas, tapped off further up the barrel, could reach the head of the piston, the latter had finished its bounce, and was traveling forward again, so its direction of travel had to be reversed by the expanding gas, instead of the gas accelerating a bouncing piston to the rear. This required a much larger volume of gas than could be provided by an port in the gas regulator."

It could be that the movie prop bren experienced a hangfire and a firing pin/piston bounce. The increasing pressure caused the unsupported primer to flow back/tear itself loose, to then release gas back into the breech. Another possiblity as you noted, is that a piece of the primer tore loose after round one, and then jammed itself into the firing pin slot, to then be rammed into the primer of round number two upon action closing.

It does appear that your issue is with the aged ammunition, not stored under ideal conditions. The use of recently manufactured ammo is probably your safest bet, as a person cannot judge primer quality on the basis of appearance alone.

Quote:

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Originally Posted by mrspeel

The hang fires, piled metal, and short recoil, were explained by the following theory: "in effect, each cap had fired at the protrusion of the firing pin, but the duration of the hang fire was such that the bounce of the piston had permitted almost full withdrawal of the firing pin before the rise of internal pressure, which was normal, had forced the indentation in the cap back into contact with it. by the time the gas, tapped off further up the barrel, could reach the head of the piston, the latter had finished its bounce, and was traveling forward again, so its direction of travel had to be reversed by the expanding gas, instead of the gas accelerating a bouncing piston to the rear. This required a much larger volume of gas than could be provided by an port in the gas regulator."

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Are they saying that the piston/bolt carrier has bounced rearward the few thou required to let the piston post release the firing pin to be withdrawn due to the firing pin spring? And then before the return spring has had chance to close the piston/bolt carrier again the gas flow has cought up and forced the working parts to the rear? That was a real clever armourer who worked that one out.

Quote:

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Originally Posted by mrspeel

Back in the day, when it was legal to shoot the Bren in Canada, as a converted auto (ie semi only), I experienced a couple of issues with surplus ammo in an Inglis Mk1m. It was '5o's era 'GB' mk 7 ball, on stripper clips, in slings, pulled straight out of the case. While the ammo appeared bright and clean, it produced hang fires and short recoil/feeding failures. After I retrieved my cases, I noticed that the bren firing pin "indent"was now an "outdent". The metal was "standing proud" on the firing pin, like a square triangle.

What could be the cause? Primer, powder?

To quote Major LM Yearsley, from a UK May 1990 Guns Review article" if the firing pin can bounce, so can other moving parts of a weapon mechanism. This applies to the piston of the gas operated machine gun. This, in combination with hang fires, can produce a pattern of behavior which can lead to the user drawing quite misleading conclusions as to the cause."

The Major goes on to write that "In the early sixties, a complaint of weak ammunition was received from the Middle East, in connection with the .303 bren. Short recoil, due to insufficient gas, was suggested by both the user and the local investigator, as correct functioning proved to be impossible, even with the gas regulator set to its larger hole.The gun and a sufficient sample of the ammunition date of work in use, were sent home for investigation."

The Major reports that the reproof confirmed the ammunitions working pressure was within specification. The fired cases, both those returned, and those collected, showed "very severe piled metal, the deep impression of the bren firing pin standing, in many cases, almost as proud of the cap surface as it had originally indented".

The hang fires, piled metal, and short recoil, were explained by the following theory: "in effect, each cap had fired at the protrusion of the firing pin, but the duration of the hang fire was such that the bounce of the piston had permitted almost full withdrawal of the firing pin before the rise of internal pressure, which was normal, had forced the indentation in the cap back into contact with it. by the time the gas, tapped off further up the barrel, could reach the head of the piston, the latter had finished its bounce, and was traveling forward again, so its direction of travel had to be reversed by the expanding gas, instead of the gas accelerating a bouncing piston to the rear. This required a much larger volume of gas than could be provided by an port in the gas regulator."

It could be that the movie prop bren experienced a hangfire and a firing pin/piston bounce. The increasing pressure caused the unsupported primer to flow back/tear itself loose, to then release gas back into the breech. Another possiblity as you noted, is that a piece of the primer tore loose after round one, and then jammed itself into the firing pin slot, to then be rammed into the primer of round number two upon action closing.

It does appear that your issue is with the aged ammunition, not stored under ideal conditions. The use of recently manufactured ammo is probably your safest bet, as a person cannot judge primer quality on the basis of appearance alone.

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My first question when I arrived, was "What ammo were you shooting with ?" When I found out it was old 1950's stuff, I suspected something of that ilk had happened.

I supplied them with some modern privi-partizan ammo which cured the hangfire problem.

Thanks to all the Bren experts for their diagnosis of the problem
It is very much appreciated.

Gary

The breech block, piston and piston post in a Bren cannot bounce in the mechanical sense of the word.......... Shall I elaborate? It's going to get pretty heavy but....... For a start, it's nothing to do with the gas port or gas regulator setting OR HANGFIRES unless there is a hangfire and someone is quick enough to re-cock the gun.

At the moment of firing, the breech block is positively locked, up in front of the locking shoulder in the body. The firing pin is driven forwards by the piston post which is carried forwards under the weight of the stored energy in the return spring and the inertia of the mass of the piston post, piston and the piston extension (the PP/P/PE). At the instant of firing, the firing pin is still travelling forwards until it protrudes between .040" and .050". At which point the forward moment of the PP/P/PE comes to a DEAD stop. This sudden stop is caused by the front rounded face of the PP striking the internal front rounded face of the breech block.

This is the only thing that causes the PP/P/PE to stop. There is NO other feature that will cause the PP/P/PE to stop. Firing pin bounce or any other bounce is a red herring because the whole mass of the PP/P/PE is effectively cushioned by the PP/P/PE hitting the the striker which strikes the soft cap which coincidentally at the same time fires the round.

The Bren had a couple of failings but 'firing pin bounce' was not one of them or believe me, we'd have heard about it PDQ! Can anyone explain a Bren gun that operates on a short recoil system....... It's long stroke gas. Am I missing something somewhere or can someone point me in a safe direction?

What say you Tankie, Son and Skippy. Get your thinking caps on and EMER's out! Short recoil................................... I must be barking!

From experience I venture to say that most alleged "out-of-battery" incidents , when fully investigated by competent examiners, turn out not to be "premature" at all. Rather, they relate to some anomaly that occurred AFTER an otherwise normal firing pin indent.

M

Quote:

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Originally Posted by Peter Laidler

The breech block, piston and piston post in a Bren cannot bounce in the mechanical sense of the word.......... Shall I elaborate? It's going to get pretty heavy but....... For a start, it's nothing to do with the gas port or gas regulator setting OR HANGFIRES unless there is a hangfire and someone is quick enough to re-cock the gun.

At the moment of firing, the breech block is positively locked, up in front of the locking shoulder in the body. The firing pin is driven forwards by the piston post which is carried forwards under the weight of the stored energy in the return spring and the inertia of the mass of the piston post, piston and the piston extension (the PP/P/PE). At the instant of firing, the firing pin is still travelling forwards until it protrudes between .040" and .050". At which point the forward moment of the PP/P/PE comes to a DEAD stop. This sudden stop is caused by the front rounded face of the PP striking the internal front rounded face of the breech block.

This is the only thing that causes the PP/P/PE to stop. There is NO other feature that will cause the PP/P/PE to stop. Firing pin bounce or any other bounce is a red herring because the whole mass of the PP/P/PE is effectively cushioned by the PP/P/PE hitting the the striker which strikes the soft cap which coincidentally at the same time fires the round.

The Bren had a couple of failings but 'firing pin bounce' was not one of them or believe me, we'd have heard about it PDQ! Can anyone explain a Bren gun that operates on a short recoil system....... It's long stroke gas. Am I missing something somewhere or can someone point me in a safe direction?

What say you Tankie, Son and Skippy. Get your thinking caps on and EMER's out! Short recoil................................... I must be barking!

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Peter,You put it quite clearly & Sucinctly. I can add nothing from my Armourers expierience & knowlege, that you havent already covered. As you state, 'We WOULD have heard about it'! Others here on the forum may possibley be unaware of how the system works in Service with our Tech publications available to the Armourers & all R.E.M.E Tech Personell. IE> E.M.E.R's, A.E.S.p.s, I.S.P.L,s Etc.
For the uninitiated: One of the things we expirienced as Service Armoures was Imeaidate instructions & also Miscellanous Instructions. These were sheets forwarded to units to insert into our Engineering Instructions Manuals (E.M.E.R.s) for us to execute any modifications or effect a different style of repair. This alleged Firing Pin probelm would have been an 'Imediate Mod' & If of such a dangerous situation. The Mod Inst Sheets would have been proceeded by a Signal sent out to ALL units in the Armed Forces. Even overnight if deemed nessacary, so that all equipment could be quarantined for safety & not used until the mod had been executed. Or the equipments inspected for faults/ defects or indeed the mod kits fitted.
All the 'Blurb' from that 'Officer' in the posted report, was interesting to see. BUT, as you have clearly pointed out a load of old B****ks! MOST Officers in almost ALL Senior Armourers Expierience, are desk wallahs & have virtually no indepth Technical 'Hands on' exposure to working on equipments (Peter is ONE of a few exceptions here, as he has climbed up through the ranks from a Humble Craftsman (Private Soldier) to Warrant Officer level. And then through his Tech abbilities & immense skills, been Commendably selected for promotion through Commisioned Officer Level) a LOT of Officers seek to gain attention to thier careers by Writing reports to get themselves a name & seek to become 'Acknowleged Experts' for this path of chosen action. In a LOT of cases, they certainly DO get themselves a name, but unfortunately, it's not really one they were originally seeking!.........LOL! The Bren/ LMG is one of THE most relaible & Battle proven weapons of our time. A LOT of time has passed since it's original introduction, & also the bugs ironed out until it has perfomed with legendary reliability & affection. Anything connected with Breech expolsions or other failures after all this elapsed time is USUALLY associated with Ammounition. You cannot get better praise then from Armourers, or indeed the intended End User. I have heard nothing detrimental spoken of a derogatory nature from the Good Old Infanteer. However, I have heard a LOT of derogatory things about SOME Officers!............LOL! Peter, I KNOW you will take this in the spirit it is writtern, & also be aware that this 'Comment' is certainly NOT directed at YOU! LOL! Cheers.

I have some Pakistani .303 belted for Vickers that routinely produces horribly extruded primers when debelted and fired in a Bren. The problem disappears completely when decent ammo is substituted. Greek HXP and Norma military come out looking perfectly normal.

So much for bolt bounce.

M

Quote:

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Originally Posted by MGMike

I have some Pakistani .303 belted for Vickers that routinely produces horribly extruded primers when debelted and fired in a Bren. The problem disappears completely when decent ammo is substituted. Greek HXP and Norma military come out looking perfectly normal.

So much for bolt bounce.

M

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Mike, It is a known fact that OLD/Stale Ammo produces high & unstable pressures at differing tempretures. Resulting upon occasison in much higher breech pressures. This can possibly also lead to primer caps blowing out of the base of the round. You may possibly be aware that bren Breech Block faces were later modified with TWO holes in the front cartridge recess. It was for this very problem, to direct the resultant gases from the round away & sideways from the users face & the potential for excessive force. To drive the working parts rearwards & consequent damage or injury! Some cases have also ruptured due to this ageing problem with old Ammo as well. The metal structure of the brass changes with age which does not help with higher pressure involved! As you later discovered, fresh/newer production Ammo cured the problem! In general terms, there is enough 'Meat' around the sides & breech area in the magazine vercinity to enable the gun to withstand a breech expolsion. or ruptured case & resultant 'Blowing out' of gas/Metal downwards through the ejection opening & upwards out of the mag opening to direct this unexpected force away from the user. But, If you have ever expirienced actual breech explosions, they MOSTLY all differ in small ways due to differing defects occuring at a particular time. BUT, this does NOT detract from the fact that you REALLY dont want to have one if it can be avoided! You only have one set of hands, eye's, Etc, Etc.........

A few years ago I saw that we were using some old RG-69 7.62mm belted ball in our GPMG's. I spoke to the ammo techs, in passing, who said that it was old war stocks being rotated and used for training. Waste not, want not. But it goes to show that it's not the AGE that matters too much but how it's been stored

Quote:

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Originally Posted by Peter Laidler

A few years ago I saw that we were using some old RG-69 7.62mm belted ball in our GPMG's. I spoke to the ammo techs, in passing, who said that it was old war stocks being rotated and used for training. Waste not, want not. But it goes to show that it's not the AGE that matters too much but how it's been stored

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yes, I recall when I used to work for a certain manufaturer who make .50 Cal MGs. We bought a Million rounds BACK from the M.O.D at @ 1p a round! we routinely used this for function testing at Lydd ranges. It is used so much by 'This Company' that they have thier own dedicated .50Cal range! It was old observing ammo, the type that make a brilliant flash when the head strikes a target. Well, it had been stored outside under trees for YEARS in direct sunlight, Bird crap Etc Etc, NOT ideal conditions! The magnisum in the tip had 'setteled' & it was the norm for round to expode approx 2 ft from the muzzle when firing. This resulted in a half moon shape of copper jacket shards of 'shrapnel' at the forwards end of the barrels about four feet in front on the ground. The eratic boom, bang, Phut, Bangs that were becoming the norm were unsettling at first. But after a few hundered rounds you got used to it & the violent shock waves from those exploding rounds! We were not bothered about accuracy, it was function testing the guns that we were interested in.
The cores went down the range ok but obviously were not too accurate! However, it was impressive to still observe a VERY good beaten zone at the impact area through Binos'!
Yes, storage IS important. It DOES affect how ammo perfoms. Accurately & Safely!...............

In the case of the Pakistani .303, I have not chronographed it but I don't think the cause of the extruded primers (in some instances the rectangular firing pin indent was peeled open like a sardine tin!) was elevated pressure. I did not detect any of the normally associated signs of high pressure or irregularity in the cyclic rate or cadence, felt recoil, gas regulator setting, or appearance of the extracted brass.

I believe the ruptured primers resulted from a combination of aging ("seasoning", i.e., embrittling of the copper primer cups), coupled with an incorrect alloy or improper procedures used in their manufacture.

In my view three factors determine the life and serviceability of ammunition: age, quality of manufacture and storage. Assuming a high level of care in manufacture, a long shelf life can be expected, but it is undeniable that the chemical compounds used for propellants and primers start to decompose from the day they are made, and there will eventually come a time when ammunition, no matter how well made or stored, will become unserviceable. A huge variable is the quality of manufacture. A little contamination during manufacture will kill a primer in short order. The selection of metal alloys used in cases and primer cups, and the care with which they are drawn and annealed, also greatly influence the quality and longevity of the finished product. If the bullets and primers are well sealed, and the cartridges do not come in contact with water or acidic paper, moisture is not so much a problem as temperature. Aberdeen PG has published tests demonstrating that degradation of performance from poor storage is largely attributable to excessive heat.

M

Hence on almost all British manufactured Ammo, the stenciling of 'Keep out of direct Sunlight' (Heat). This definately would affect the condition of ammo during storage & resulting deterioration.
That is THE reason why, ammunition is routinely rotated. Keeping stocks fresh & using older stuff for training purposes. ROTATION of War Reserve stocks to Training, & then War Stock Replaced with new manufacture.
If you have ever been in Any Ammo long term storage bunkers, you will have noticed they are always 'Cool' inside. I have been to a large one in Germany to get 81mm Mortar ammo for a unit shoot. There was even a shimmering shine comming off the concrete walls. Phosphorus from smoke bombs, now how the hell did that get there when ammo is SEALED VERY well in it's packaging!.........