Just a snippet of Bren info for you Bren fiends............

[Kev G]

Forgive me for saying but the front end doesn't look very 'unissued' ?
I have never seen another M39/ZB39 before with a sleeved gas cylinder (not that I have seen that many !) looks more like a local modification /repair ?
If it was new made surely they would have just not machined the front holes in the cylinder ?

ATB Kevin

[Peter Laidler]

Yep, got that and can see now from one of the pics

[c310pilot]

Forgive me for saying but the front end doesn't look very 'unissued' ?
I have never seen another M39/ZB39 before with a sleeved gas cylinder (not that I have seen that many !) looks more like a local modification /repair ?
If it was new made surely they would have just not machined the front holes in the cylinder ?

ATB Kevin

I have the complete kit and it is perfect. Not a scratch on anything, deep blueing, and the barrel is the brightest bore I have ever seen in a gun over 20 years old. It looks just as nice as my AR barrel. Also the receiver section is mint except that weird sleeve. The biod fits very tight and their is no scoring or radial scraches from where I bipod would have rotated.

[John Sukey (Deceased)]

I'm Not worried, I have a spare bipod sleeve!

since I don't have a friendly gubmint supplying the free ammo, I doubt I will ever need it.

[MGMike]

I expect that you have all heard of the problems with the first Mk1 Bren guns. Basically, and without boring you to death, the gas deflected from the barrel and gas plug hit the head of the piston. In an effort to get rid of the crud and shi...... er, metallic fouling and carbon, there were two lots of 6 holes to allow it all to escape. Alas, one set of holes was under the rotating SLEEVE, Bipod which after 25 or so rounds, solidified on the outside of the gas cylinder. So, to free it off, you twisted it left and right a few times. The trouble was that in doing so, the hard carbon quickly wore away the outside diameter of the gas cylnder and the inside diameter of the bipod sleeve. Allowing so much gas to escape that the gun failed to work!

...!

Peter: Please help me to understand this. Is it correct that as to the FRONT set of holes, the original design contemplated that NO gas would be vented from them? Were the holes there solely to provide pockets for fouling to collect that would then be broken up by rotation of the bipod, and thereafter blown out of the REAR set of holes?

M

[Kev G]

Not sure if Peter is back yet so this should answer your question.

ATB Kevin

[MGMike]

Kevin: Thank you for that link. I hadn't realized it had been patented (though that makes a lot of sense).

Was the failure of this invention principally due to the properties of cordite? Other propellants don't seem to generate such hard carbon or as much of it. Reason I ask is that my Czech "Bren" does have the early-pattern gas cylinder with the holes under the bipod sleeve. I haven't had a bit of trouble with functioning, but then I don't use cordite ammunition.

M

[Peter Laidler]

I'm sure that it was to to do with the properties of cordite residue when it is cold. But as an engineer, where the properties of cordite are well known and researched and readily available for all to read up, then the theory put forward in the patents really defy common snse or as we say in England, defy the bleedin' obvious. It's a bit like saying that when you decoke your car engine (I know we don't do it nowadays but.....) we'll vent all the hard carbon fouling from the valves via the valve guides or better still, the wheel bearings

Anyway, the end result was known in March 1940 but instead of fixing it immediately, they used a palliative as oposed to a cure. And to heap further problems onto the poor Bren, the palliative just caused another problem. But this time, it didn't just cause ONE problem, it caused TWO problems............

Thanks for bringing up the patent KG

[MGMike]

Peter: Thank you for the further reply. Part of my uncertainty emanated from the description in Dougelby to the front holes as "gas relief ports", which is misleading. Certainly "gas relief", while it may have been a result, was not the intention. In theory it does not seem like a unreasonable idea, provided the fit between the cylinder and the bipod sleeve were close enough to allow a perfect shearing without leaving residue (but then the bipod would be too tight to articulate easily). They even provided little pockets between the holes for some outside residue to collect, and any wear --initially at least--would have been confined radially. Obviously it didn't work out that way.

Which leads me to a related question. With cordite, the troops must have worn out piston heads and gas cylinders at an alarming rate. If a little bit of blow-by was enough to cause short recoil, how did the Bren ever win its reputation for reliability? If the gun were not immediately cleaned before it cooled, there would unavoidably be the same hard debris in the cylinder behind the piston as well as in front of it. Similarly I've seen assault rifles (and a Lewis gun) that would "lock up" overnight.

M

[Peter Laidler]

One of the problems with the Bren was exactly as you have mentioned it MGM! The front gas vents were there to allow the gas/carbon and other residue such as cupro nickel, brass and copper to vent after initially striking the face of the piston. But strangely, while pistons did wear at the piston face, I don't remember it as a serious problem with the Bren as ther were really hard chromed on good quality steel that wasn't exactly 'stainless steel' as defined. Can any other Armourers out here remember it being a problem? We could and did re-face Bren piston faces back by a few .000's of an inch and have them re-hard chrome plated where the facilities existed but they were a bit like L1A1 rifle pistons where while it COULD be done, it wasn't done very often. Usually at the big Base Workshops when a whole batch had been gathered together. But I digress..............

One other problem that manifested itself with he Bren was that a ring of hard carbon would form in front of the piston, around the interior of the front gas vents. As a result, it'd slowly build up and rearwards until the gun became sluggish and eventually, the gun would fail to fire due to the inbuilt mechanical safety. This was the fact that the breech block was fully locked in front of the locking shoulder, and before the gun could fire, the piston, piston extension and piston post have to move forwards another 3/8" or so (I forget the exact amount now) to strike the firing pin and then fire the round. If the piston was prevented from going FULLY forwards, then even a stoppage during its last .050" of travel would prevent the gun from firing. That's all it took and you started to have intermittent stoppages.

There were MANY palliatives that didn't really cure anything but caused more problems. The gun only truly earned its good name when the Mk2 came on stream and the old Mk1's were modified.

I'll give you another example........... It was thought that if you opened up the gas port from .14" to .148" (someone correct me if I'm wrong but I forget the exact figures) you'd get a bigger volume of gas through to operate the gun. Correct....., according to Boyles laws of course! These larger diameter ported barrels are called Mk1*. This worked and cured the loose bipod sleeve/venting gas/stoppages problem but in itself, caused another problem. While the bipod sleeve was still relatively tight and there was NO gas loss, the now EXTRA gas sent the piston post back to unlock the breech block so bloody hard that it shattered the piston post spring. And yes....., that's the reason why there is always a spare in the spare parts tin. It also mushroomed the rear end of the Mk1 piston post plunger over as the piston extension battered the rear end into the back end of the piston post. Result.........., you had a broken spring AND the end of the piston plunger spring mushroomed over so that the gun crews couldn't get the plunger out of the broken spring in order to replace it.

The result of that was a shorter, Mk2 piston post plunger and a Mk2 piston post with a slightly different internal configuration.

Then, when they'd done this, something else went wrong because presumably someone at the time forgot that in Engineering and basic school boy physics, something mechanical ALWAYS affects something else.

On the subject of the patents regarding this extra ring of vent holes, I've been reading them carefully thanks to KG showing them (and incidentally, go through this in great detail in the forthcoming book...........). It's absolutely true that you can't patent the laws of physics but you can patent virtually anything with the correct use of words. And I think this is this frill, if not an absolute fraud was patented.

Phew....... not such a quick reply but it's the sort of thing tha you have to mention to keep the current generation of design engineers on their toes