7.62mm barrels

[Peter Laidler]

BREN BARRELS.........

This is a short article, really written by me based on nothing more than my thoughts and admittedly never having done it. But as you’re well aware, being an old school Armourer and engineer I’m a big believer in and having brought up in the era of ‘......where there’s a will, there a way’ Or in my speak, there’s a SIMPLE way. That said, I expect and hope to see some alternatives to what I’m suggesting. Thanks to Joe, Vince, Tom H, Tiriaq and others too.

What the US Bren builders are short of isn’t Bren barrels per-se because the place is awash with new and used/shot-out/clapped out or otherwise knackered .303” Bren barrels...... but more to the point, Mk2 barrels. The rub is that it’s not Mk2 .303” barrels you want, it’s 7.62mm L4 type barrels you want. What is lacking is the will - and where there’s a will, there MUST be an easy way. Ignore Mk1 barrels from this point forwards

We know from earlier correspondence that 7.62mm rifled tube is available from most of the barrel makers. We also realise that making 7.62 Bren barrels from scratch is......look chaps, unless you are millionaires with guaranteed sales in the thousands, forget it and get onto the real world we all inhabit. With all that intricate machining and equally intricate, accurate and delicate inter-related indexing of the many this that and the others - it ain’t going to happen at a realistic price, believe me. But what could simply happen is this. Sat with a barrel across my lap yesterday evening, I think that there are 13 indexable or inter related accurately machined features on a barrel, all of which render others or all hopeless unless they're dead accurate. I mean, what's the point of a canted foresight or a misaligned positioning slot?

Let’s take a bog standard shot-out or otherwise knackered Mk2 Bren barrel. The 4x principle diameters are this.
BREECH that intrudes into the main body: .906” dia for a length of .9” or so
LOCKING THREADS: 1.25” dia for a total length of 2”
UP TO CARRY HANDLE: 1.175” dia for a length of some 3.75”
CARRY HANDLE TO GAS BLOCK: 1.1” dia for a length of some 6”
GAS BLOCK TO MUZZLE: .88” dia for a length of 6” or so.

It is these diameters that should concern us but more to the point, the initial .906” dia and the final .88” diameters

Strip the barrel only leaving the gas block in place. (But to be honest, if you have a good capable press, you could even remove this too. It’s up to you. I would leave it. After all, it ain’t broke, so don’t disturb it!)

THIS is what you do and you don’t need to be careful how you do it either. You bore your existing 303” Mk2 barrel out from end to end to .7”. The drill that you’re using will naturally follow the path of the existing .300” dia pilot hole. From this you will see that EXTERNALLY the barrel remains EXACTLY as it was. And luckily for you every one of those mega important datums, accurate machining and inter-related indexing features are still intact. Simply by saving those important external features, you’ve saved yourself hundreds of $$$$$’s in future time and effort. So far, so good.......

Now you machine out the breech end to a diameter of .920” for a depth of 4” or so. But this time you’ll notice that you have machined away the complete breech section that seats into the main body of the gun. But don’t worry......., more about this later!

Your machinist with advice from a metallurgist should now machine down your 7.62mm rifled barrel blank so that the blank is .920” at the rear end, extending for 4” plus a bit and .700” for the remainder of its length. What we want to do now is take advice from a metallurgist as to the expansion of the barrel in a furnace into which the liner will drop. After it if in place the contracting outer barrel will grip the new liner absolutely. If done correctly, there is not even the remotest chance that the liner will ever move because hereafter, the liner will expand slightly faster than the and........... Anyway, take my word for it lads, the liner will remain totally and absolutely locked in place by the super strength of the radial grip over the barrel length. How do I know this....... Simple, that’s what they did with the satellite liner in the GPMG chamber*!
*they failed but for another reason.....

What you have to do now is to machine the new protruding breech end for diameter and length to suit your gun body. At the muzzle end you follow the tongue recesses for the flash eliminator rearwards and accurately mark them out for the flash eliminator that will be moved slightly rearwards to suit its new 7.,62mm barrel (length from gas block to end of barrel EXCLUDING f/elim = 5.5”). Ream the chamber to suit your CHS, crown muzzle, slide on flash eliminator and using existing hole in gas block, carefully drill out gas port.

There....., it REALLY is as simple as that. Some have suggested that a breech end dia of .9” is insufficiently safe for a full power 7.62mm cartridge. I say bollxxxs..... That’s how they already are and additionally, the barrels are already UK Military proofed as stand-alone. That is, proofed NOT fitted into the protective ring of a gun body. So if it’s good enough for UK Military proof, then it’s good enough for us. Likewise, some say that the walls of the new liner will be too thin. Once again, what a load of fuzzy-logic bolloxxs. The whole length of the liner is tightly surrounded by the strong full diameter of the existing barrel. And to illustrate the point, look at the diameter of the last 8” or so of an L1A1 barrel. Point taken?

Like I say, where there’s a will, there’s a way. And hopefully I have proved here that from a simple engineering point, there is a simple way. So let’s not hear any more waffle and crap about there being a shortage of 7.62mm Bren barrels. What there appears to be is a shortage of will.

Please feel free to come back with any constructive criticism and make this a lively debate

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