Sneaking in a quick Bren question for Mr Laidler...

One of the elder statesmen over at gunboards is looking at making his Bren cheaper to use for trimming the cactus outside his front gate. In answering another poster's Bren Q, he added his problem to do with making the Chinese 7.62X39 kit cycle....

"Yes there are 4 positions, but the No2 position is reccomended. Only when the gun gets really dirty do you go to three and four. But then we are not shooting ours in a war, so we can clean them regularly.
However I am still trying to make mine work with 7.62x39. Have the chinese barrel, gas regulator and other bits to make the AK mags fit I do have spare return springs and may eventualy try shortening one. The gun will load and fire but not keep going. However it still works fine with .303

Oh by the way the gun DOES NOT ruin brass."

Any thoughts?

Mmmmmm. There are two major things that make a Bren stop Insufficient energy available to unlock, extract eject and cock. The second is insufficient energy to feed, load, lock and fire. Cause of 1 is insufficient gas and cause of 2 is insufficient stored energy in the return spring. From that, the answer is that we need to know at what point it actually stops. Any further thoughts Son?

One point that isn't well known regarding Brens is the friction imparted on the breech block by the action of the locking ramp on the piston extension. The ramp forces the locking cam at the back of the bolt to bear hard on the underside of the body. This is deliberate friction that gives the Bren its slow (?...., well, relatively slow....) rate of fire. It eats up a lot of the stored energy held within the retutrn spring. So on the face of it, the spring can seem perfect but is too weak to overcome this additional friction. That's enough of the physics lesson!

I'm thinking tha this is a Semi Auto conversion as he says it loads and the fires. If it is, (I'm not fully conversant with the SA conversions) does that not mean theres a 3rd spring to overcome when the parts are forced rearwards by the gas pressure? If I was this guy, I would go to the 3rd gas setting to see if it worked and maybe even no.4 if required.

Also, which Mark is it, whos the manufacturer and whats the serial number? I ask as depending on the Bren, the gas cylinder to bipod sleave may be worn and allow some gas to escape. The .303 may be ok but the 7.62mmx 39 dosnt have the power to lose and operate satisfactorily.

BP is right. The only thing that can make this guns working parts move to the rear is a huge blast of gas. If they ain't going far enough it means that they ain't getting enough gas. But as we showed with some simple experiments with the AK gas system (brilliantly thought out and an example of pure mind boggling simplicity.......), there comes a critical point, due to boyles law when the m/v of the bullet is SERIOUSLY compromised.

There is a simple laboratory experiment where you can show the volume of gas generated by an amount of propellant. I'm not a chemist but used to enjoy this bit of chemistry. But above my head!

Yes- I was telling him that the problem would be insufficient gas. I mentioned enlarging the gas system but he said the kit was supposed to be a proven item, and the gas port and regulator were already much larger than their .303 counterparts. I said that my own workings with a similar but more modern weapon regards rates of fire we discovered there was only a couple of RPM difference between a totally worn out (very weak) return spring and a new one, and that cutting a return spring down wouldn't do much except endanger it's ability to return to lock.

Brit Plumber- thankyou for your input, The gun is full auto. I too question the ammo's ability to do the work...

Does the Bren, like the similar action in service currently, like to be soaked in oil to function... I am wondering if a combination of lack of lube to minimise the friction of unlocking and also gas leakage might be his drama.

I have had no experience with Brens, so anything anyone can offer here is appreciated.

The Bren doesn't run on a lot of oil Son. It's really the piston extension slides in the body, the locking cam surfaces and importantly, an oil coating on the inside top surface of the body where the top rear surface of the breech block frictions.

You COULD tell him to get his head out of the sand regarding the perceived notion that it's a tried and tested system............ It's clearly not that well tried and tested because it ain't working. If the breech block and piston aren't going fully to the rear and touching the buffer plate, then there isn't enough gas. It's really as simple as that. He could try to eliminate some of the not so obvious areas, like fitting a new gas cylinder and piston but as I said, it'll be insufficient gas.

Next time you're here in the land of the Poms Son, we'll get you in the Armourers shop for a day with a few Brens and L4's

As the 7.62x39 AK conversion was utillised by the Chinese on ZB's and Brens it would seem to be a proven modification design.
Although the gas porting (what diameter is the exit hole on the gas regulator housing ?) is enlarged to compensate for the lesser cartridge there is also slightly less energy required to cycle the gun.
The 7.62 x 39 round being shorter there is a second bent ground into the piston post about 18mm rearward of the 303 one so slightly less energy required to compress the return spring to enable the sear to engage or strip the next round from the mag.
If it is a 'genuine' Chinese conversion using the equivilent military AK round and carbon free and not leaking gas it should be good to go.
My concerns would be "supposed to be a proven item"........?

ATB Kevin

I would be most interested to see a GENUINE Chinese converstion to 7.62 x 39mm. To examine how they got over the combination of difficulties in getting a Bren series to function correctly. There definately ARE a number of variables as to how a Bren would function properly. Some covered here already. Gas bleed, Worn componants Etc. all pretty obvious really. My concerns would be. The 7.62 x 39mm Round is a LOT less powerfull then the Original 7.92mm/ .303" class of round it was DESIGNED around, in the first instance. With a significantly weaker round to overcome friction/ gas loss/ worn componants, spring pressure , Etc Etc.
It is indeed quite a bit to ask of such a modest round! It has been sugested by Kev that the Chinese did indeed overcome the problem. I would be very interested from a Technical viewpoint to see how that was achieved.
I like Peter, am FIRMLY of the opinion the weapon most OBVIOULY needs gas to correctly function cycle. IE: Has the gas post UNDER the gas block in the actual Barrel been enlarged?
I am certainly NOT a Mathmatician! But working out on paper all the other variables. IE: Mass, spring pressure, wear, gas loss pressure, Etc & loading them in the equasion would be mind boggling to me!
It IS asking a LOT from a significatly lower prressure round to RELIABLEY function cycle a Bren! Im not saying it cannot be done, but i have my own doubts. There may possibly be some drastic machining done internally to relieve weight, Etc? Without seeing one, it's difficult to state for certain. Agreed?
We have the opposite end of the spectrum with the FG 42 dont we? a TOO powerfull round for the intended role of assualt rifle! BUT, If it had been made in 7.92mm KURTZ at the time..........
OR, Indeed, THEN, a working postwar coversion into 7.62 x 39mm IF, there were enough FG 42's about to convert without ruining one because of it's rarity!.......No Problem!

https://www.milsurps.com/images/impo...02/chink-1.jpg

Given the fact that this is a "kit" derived from a Chinese-made or converted barrel, I think I would start by very carefully examining the chamber in strong sunlight and, if necessary, making a cerrosafe chamber cast. If the chamber is rough, or scored or of improper profile it could be causing enough drag on the fired cartridge case to emulate insufficient gas.

M

This is one of those imponderables.................. We're not actually looking at the problem as such, but the variables. Give us your views on these Chinese conversions MGMike. Have you seen any/many? They look interesting.

I always remember back to 15 or so years ago when a load of blank ammo was doing the rounds. It was from.............. well, nobody ever could tell but the end of the boxes was marked green white green and some wag suggested that it was Nigeria - or Kenya or, well, anywhere really. But even the best Brens and GPMG's coped to struggle with it most of the time. We thought it was filled with chipatti powder but every so often you'd get one filled with TNT.............

What I'm saying in a very roundabout way is that not all 7.62 x39 is made to NATO spec!

Peter: I have no experience with the Chinese conversions and have never even examined one closely. But I would note that it was a makeshift conversion, at a time when the Chinese imagined it was worthwhile because they had nothing better. The Bren is too much gun for the 7.62x39mm. The workmanship of such improvisations is always suspect, as is its condition by the time it was mustered out, cut up, and sent to the USA.

Clearly other ammo should be tried, as that is a huge variable. However, if the gun is getting plenty of gas, but it's still not running, it's time to look elsewhere. That's the reason I'd suspect the chamber. I have seen a Czech ZB26 that would not cycle, though it had been successfully test-fired a few months earlier. Closer examination revealed that the test-firing had been with obviously corrosive-primed ammunition --which left a thin haze of red rust in the chamber. That was enough. It slowed down extraction sufficiently that the bolt only half-cycled and re-chambered the swollen fired case, which was then firmly stuck.

Anyway, it's just a thought.

M

Clearly other ammo should be tried, as that is a huge variable. However, if the gun is getting plenty of gas, but it's still not running, it's time to look elsewhere. That's the reason I'd suspect the chamber. I have seen a Czech ZB26 that would not cycle, though it had been successfully test-fired a few months earlier. Closer examination revealed that the test-firing had been with obviously corrosive-primed ammunition --which left a thin haze of red rust in the chamber. That was enough. It slowed down extraction sufficiently that the bolt only half-cycled and re-chambered the swollen fired case, which was then firmly stuck.

Anyway, it's just a thought.

Mike. Whatever happened to Pre Firing checks? If that had been done properly, the 'Rusty Chamber' prob would have been picked up & cleaned prior to usage. This is an absolute MUST with ANY Firearm before using it really! Rusty chamber = Hard Extraction. Also resulting in failure to Function!................Naughty User!.....Lol

M[/QUOTE]

It wasn't my gun.

M

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Originally Posted by MGMike

It wasn't my gun.

M

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.........And you never enquired about the points I mentioned to THAT user before HE fired it?..............Recap: ANY Firearm, ANY user, BEFORE Using (ANY)......
I think that firing session was flawed before it even started then Mike, from what you have told us! If the guy who OWNED the Gun & it was HE who used it without doing a VERY Basic thing like Pre Firing checks.
How would ANYBODY, with respect. Put any credance to the test session if the basics have been ignored. Also, it would cut down on areas of a 'Process of Elimination'!
Also, To MY mind. If it it were ME who had manufactured & sold these items as you say. It was a kit, was each kit fired & function tested to PROVE the set? ..........MMMMM..Smacks a bit of Enthusiastic Amature or non proffessional to me!..............Are you able to Elighten us Mike, Please............

Tankhunter: I would never presume to enlighten you.

M

Quote:

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Originally Posted by MGMike

Tankhunter: I would never presume to enlighten you.

M

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Mike, You Humble me Sir! If we are all Honest & have open minds. We can ALL be big enough to be aware that even though we may amass a large amount of knowledge.
There is ALWAYS somthing we can learn! People I have worked & come in contact with have laid the Title 'Expert' upon my shoulders many times. I have been QUICK to point out that I am very knowledgable
in my Field . With gained Expierience & actual hands on events over the years. But I request that they do NOT use the Term 'Expert' towards me. The reason is VERY simple. There will ALWAYS be someone who knows a bit more than yourself. No matter how much you learn over the years. And to that end, the nice (& Interesting) thing about Life is. You NEVER stop learning!..........ALWAYS Keep an open mind!
Peter like myself im SURE. is always happy to educate & share knowledge where possible. My One Main fault (If I may term it that! & I also have MANY!) is that I do NOT Tolerate fools gladly! Peter too has this quality, BUT, is more of a Gentleman than I. And hides his internal displeasure a LOT better than I would!........Ha, Ha!

I don't think you are reading each other's posts quite closely enough...Seems like small but important points are being missed before replies are made. But if y'all want to go on hatin' on each other, I don't think this is the right place...

Quote:

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Originally Posted by jmoore

I don't think you are reading each other's posts quite closely enough...Seems like small but important points are being missed before replies are made. But if y'all want to go on hatin' on each other, I don't think this is the right place...

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JM, I dont believe the word Hate has EVER been raised on this forum? & if that is the case, I, for one am not aware of it! (In fact, sadened that that could be thought really!) If you recall, I DID raise a point on a very earler post.As to the fact that in points of opinion & debate. Things CAN & sometimes DO sink to a level that MAY be construed by SOME as critisisem. And I made the Point at the time that I am aware that some Members of Forums do get the Hump. I for one, have NEVER had the intention to upset ANYONE on here. AND, if I have, I appologise for that fact & add that I am UNAWARE of being an Instrument that MAY have done so. IF ANYONE HAS A 'DIFFICULITY' WITH MY POSTS OR ACTUAL EXPIRIENCES. PLEASE DO, LET ME KNOW & I WILL ATTEMPT TO RECTIFY THE SITUATION. I POST FROM ACTUAL HANDS ON EXPIRIENCE IN THE HOPE THAT I MAY SHARE KNOWLEDGE & EXPIRIENCES THAT MY SAVE A MEMBER A POTENTIAL FUTURE HEADACHE OR EXPENSE, OR WORSE! (& I HOPED WITH AN INTERESTING CONTENT!) IF THAT IS NOT WHAT IS WANTED ON THIS FORUM, PLEASE INFORM ME & I WILL WITHDRAW. I ALWAYS LABOURED UNDER THE IMPRESSION THAT KNOWLEDGE IS POWER. IF I AM ABLE TO ASSIST & EXPAND THAT KNOWLEDGE WITH OTHERS. I WOULD HAVE THOUGHT THAT WOULD HAVE BEEN A GOOD THING. PLEASE EXPLAIN IF I AM WRONG?[COLOR="Silver"]

Also: Please Remember, that the written word can look harsher down in print, that a friendly face to face discussion!

If you will note that MGMike's reference to a problem that developed between firings noted that the "test-firing" previous to the one he merely witnessed had been conducted successfully. The only apparent change was the corrosion in the chamber. Regardless of pre-firing checks or whatever, the problem was the problem- rust, yes? Why attack MGMike after the fact when he may have had NO control over the situation. He may have been merely asked to troubleshoot the source.

"Hatin'" may be strong, but "hasty" isn't.

For his part,MGMike, in the previous thread, jumped in w/o reading the context of the OP, and was off topic a bit from the start. In actual fact, I think Tom-M failed to maintain control of his thread, but it was interesting enough to try and bring back on track, roughly. MGMike also seems to have let the sarcasm get a bit strong.

For my part, I'm at fault sticking my nose in others' business, and so will now bow out.

I just don't want valued members to leave the forum due to interpersonal frictions. Mostly brought on by failing to carefully read what another is trying go convey.

---------- Post added at 02:59 AM ---------- Previous post was at 02:58 AM ----------

"to" not "go"- can't hardly edit in "mobile mode", sorry!

HI JM, Again, ATTACK really IS a bit strong! Lol!
No, I was not attacking at all. Merely Pointing out what my thoughts/ expirience has been on Smallarms.
I feel I MUST Reitterate also: The Written Word can sometimes look Harsher on Paper that an Actual face to face Disscssion.

A Point that looms out in your post to my mind is your usage of the word 'Rust'.
Surely Rust (Corrosion) would be caused by Inactivity & poor lubrication prior to storage.
If this is the case, then again. Is it not valid to ask if the Pre Firing Checks had been made? IE: Barrel & Chamber oiled & then wiped dry prior to firing.

At the risk of Offending (& thats certainly NOT my intention) I would add then that not ALL the facts were laid down as to the raising of the question of why this weapon failed to function correctly originaly.
Shall we agree to leave it there JM? Because I feel sure the Forum Members want to know about the more interesting aspects of Tech Questions. Than something that MAY be percieved as 'Nit Picking'. I Bow out............:cheers:

As mentioned previously, I've bowed out.

Interpret MGMike's brief post as you wish. In actual fact, I don't know that what he stated was the correct cause of the malfunction. It was working, then the weapon wasn't. Corrosion in the chamber was found, apparently recent...

I've no idea why the owner/operator didn't do a check before firing. Maybe he did and didn't see a change or saw it and didn't care.

Mind you I don't really care either. It was just a suggestion that MGMike gave for checking possible areas of drama. I've heard worse.

So. Drive on. I'm mostly here to learn. I surely don't have the depth of experience as most of you in this area, I've just sampled a broad spectrum of auto weapons over the years. I'm more of a rifle guy- but some do have selector switches, which I prefer not to use except for recurrent familiarization.

JM, best we leave it there I guess?

I will add the rider, IF, I am able to help you at all with any Tech Enquirey. Im here to help IF I can. :wave: