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

Information

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[Joe H]

Peter,

I guess I'll throw in my 2 cents. Just as you said, if you were making a lot of these barrels and were doing them on CNC equipment I doubt the machining would be a big problem. Of course all the work would be setting up the first one .

I have a small home workshop. It includes an ancient Jackson vertical mill, it has a WW II war dept. tag on it, and a circa 1962 13" x 36" Clausing Colchester lathe. My comments are based on using this equipment and the usual variety of manual indexing equip and tooling. I don’t have the ability to drill/bore the hole required or to heat the parts for full sleeving. Even with heating I think you may need a press to install the barrel sleeve. Screwed up sweat fitting is unforgiving.

I'm not disagreeing that it could be done the way you explained, It's just that I would not choose to do it that with the equip I have available. I'd expect it to take a good bit of setup and trials to get the tolerances required for your method.

I’d start out the same way with a MKII or MKI barrel and a 7.62 barrel blank. The barrel round blanks, not contoured, I have seen are available 1.2 -1.25" in dia. I would use the largest available say 1.25". 10 -12" twist.
I’d cut the rear 5” off the bren barrel, bore it to .903. Cut it to 2.15” +. Note that the .90” unthreaded section of the original barrel will now have disappeared. Machine the end of the blank interference to .9033” (my best guess for a sweat fit in the bren barrel section). Make sure the machined section will protrude at least 1” past the threaded bren barrel section. You will machine it to exact length later. Heat the Bren barrel section and press it on the barrel blank. When it cools it will be on permanently.
Now going forward the next machined section is the boss of the barrel handle. The OD will be a little over the OD of the barrel blank so you will have to sweat on a tube to increase the OD for machining the handle boss. The holes have to be indexed for the handle but it is nothing critical since they set the location of the handle in the stops. With the threads now in place on the blank it is not difficult to index the barrel for further machining. Machine the handle boss.
The next item forward is the slot for the barrel indexing to the body. It is interesting to note that many WWII barrels don’t have this slot nor do the 7.62 SA barrels. Just some turning and milling.
Next is the seat for the gas block. Simple turning but it must be carefully fitted for press fit with the gas block you are going to use. Drill & ream for the gas hole and securing pin. Turning and milling 2 slots for the flash eliminator. Finish barrel contouring, machine the rear end and chamber.
It will be a lot of work and expense but I believe it can be done.
Here is my estimate of parts and additional tooling:
Bren barrel $ 85
Barrel blank $ 80
Chamber reamer $ 110
Range rod (reamer alignment) $55
Misc Bits, reamers, etc. $100
Total Material $ 430

The gunsmith I have used to re-chamber and re-bore a Bren barrel to 8mm mauser will not reline barrels for hi -pressure cartridges. Why I don't know why and haven't inquired. Other than 22 rimfire he lists a charge of $375 and up plus $100 for a new chamber. I doubt this includes sweat fitting a new barrel liner, probably just gluing or soldering a liner in a drilled hole.

Joe

[Peter Laidler]

Thinking out aloud Joe, as I'm prone to do lately I'm thinking of using up old shot out, rusty or otherwise unserviceable barrels in this respect. So the value would be pretty well zilch. In much the same way that we'd use similar barrels for BFA. Start by cutting away the rear .906" breech end dia but you MUST protect the barrel to body surface.

A lathe with a long bed and a fixed roller head steady could support a barrel mounted muzzle end in the headstock chuck while a suitably and easily modified .5" dia and then a .7" dia drill bit could be drilled through in stages from a chuck mounted in the tailstock. Easily achieved as the .3" pilot is already there.

Likewise, bore into the breech end .9" and then .920. That is the 'old' barrel part finished. Time taken using friends large lathe 45 mts. Time to clean up swarf, cutting fluid and lathe, 1hr! But no doubt there WILL be a machine shop locally that could easily do this on a cash basis. After all, this is simply deep bore drilling a hole as opposed to deep bore fine finish boring

Regarding the locating slot on the underside of the barrel. It's true that some Canadian (or was it UK) barrels didn't have this slot. But that's because the barrel was located between the large upright ears of the Mk2 gun blast deflector. That's why they are there. It would be simple to machine off the female slot part if it wasn't needed. But don't forget that once the external parts of the barrel are machined then it's got to be stripped down for bead blasting and phosphating (and painting)

[bigduke6]

Joe, Whats the spindle bore on your lathe ? if you can get a bren barrel in and fit a spider chuck or similar on the end of the spindle then you can drill /bore the original barrel, you need to make up a drill with extension, to get an idea on tolerances and heat required try a small example.

If you can freeze the liner too it helps....

Cant say I've done a Bren barrel , but relined a few .303 Enfield barrels to .22, very similar to Peters advice. the last one I did I used an unfrozen liner instead of the one that had been in deep freeze over night, all going well until the last 1/2" had to revert to the hammer managed to get it in but just..... I left plenty of meat on the chamber end just in case.

[Peter Laidler]

The outer barrel only has to nip the inner sleeve to radially clamp it. Because it's the total area of the clamping action plus the radial compression that does the job. Having said that, there will be other methods of inserting the liner. What about modern lok-tite compounds?

[ActionYobbo]

it would be easier to turn the blank to the required profile and then populate it with the profiled parts salvaged from a donor barrel.

[Joe H]

bigduke et al,

My lathe has a thru hole of 1-7/16". Easily big enough for a Bren barrel without the fittings.

I'm not at all saying that what Peter suggested can't be done. If I were a gunsmith specializing in barrel work I'm sure I would be set up to drill & reline barrels.

I just don't have the experience to drill/ream to the tolerance required for a shrink fit. My experience with shrink fits has not been the greatest typical of that last 1/2"on your .22 cal reline. If it doesn't go in all the way you are screwed. 21-22" is a long way to drop in the liner before it seizes by being heated up by the outer barrel. And you need the furnace capable of heating a 24" barrel uniformly. Maybe dry ice for the liner. In any case unless you are experienced I doubt you will get it on the first try.

If the .9" in the rear and .7" insert is capable of handling the pressure on its own then the shrink fit wouldn't be needed structurally. Drill till the liner fits in maybe .001" clear. Even at a theoretical .001" oversize hole you would probably have to drive or press it in for that length (my best guess). Then hi temp solder at the ends and /or pins. Loctite will work but all retaining compounds/ glues will release at about 500 deg F. Typical gunsmith solder is 475, Hi temp silver solder is 1200 deg F and there are 750 deg F solders available Of course we are not building a machine gun barrel. Just thinking out loud for discussion.

I've never seen any shot out barrels for sale here. They may exist but the cheapest advertised is about $70 usually with a missing handle.

Mr E. I also considered that by sweating or soldering them on the barrel blank. I'm really not sure if it is less work that milling new ones. just another possibility.

You were right Peter, this will spark some interesting discussion.

Joe

[Brit plumber]

AFAIK, the only barrełs with out the slot are the Monotype MK2 barrels. Lithgow and Inglis Mk2 barrels had the slot.

[ActionYobbo]

Joe
drill and pin like the SKS or AK
there is enough meat there to get 4 pins in the chamber end. all the other parts only need 2.
you could pin them and them weld over the pin then finish the area to hide it.
I have used solder paste in the past to do .22 relines and it makes the job easier. I have also used green locktite to do .22 liners and thats the easiers of all but I do not think it will hold up to the heat and hammering of a semi auto centerfire

well that more than 2c worth but its good value

[Peter Laidler]

I think that it's being totally unrealistic to suggest that starting a total external re-profiling exercise from scratch using a large outside diameter rifled barrel blank would be easier (thread 6) It's totally unnecessary because you already have it - on the old barrel! What's more, it's all accurately done at the factory using the original drawings and passed by the MoS examiners. All you gotta do is to reline it!

Shot out/worn out/rusty barrels appear to be unavailable simply because by definition nobody in their right mind would a) want to buy one and b) as a result, feel the need to advertise any for sale! That's just my logical pragmatic view.#

Here's another point to ponder too. As soon as you pin a barrel with a transverse cross-pin, the barrel is weakened at that point and is only as strong as THAT diameter. (not a STRICTLY mechanically correct fact as there are certain tensile and stress related variables. But it IS weakened!)

Obviously some of the operations such as drilling out the barrel length would need to be done commercially and that would be relatively cheap. Look chaps...... the gun trade in the UK were boring out No1 and 4 rifle barrels AND BREN GUN barrels into shotguns by the thousands...... And that was with the bodies attached! What's the difficulty in boring out to.7" over .410"? Drilling a Bren barrel is simplicity itself. But this time you ain't paying for a desk bound geek to draw up the radial and lateral profile on his CAD!
Nope, I'm of the 'can do' era of graduates/engineers/Armourers as opposed to the 'its too difficult' generation. They never thought like that when they were making the Bren to start with.....