Repairing Bren Mk 1 barrel

[Richard-]

Hi All,

I'm an Australian firearms dealer and armourer. I have a registered Lithgow Bren Mk 1 with holes drilled in the chambers.

Much like the US, this doesn't make any difference to its legal status, so the gun is registered as a live firing machine gun.

I want to repair the barrels so I can live fire it. I've done a bit of research and understand that this is pretty commonly done in the US.

I have a few ideas and a CAD drawing of my proposed method - I'd like to get some feedback to make sure I'm going about it the best possible way, as I'll have to make new barrels if I screw these ones up.

Is that something we can discuss or is it off limits?

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[Vincent]

I have seen people plug weld the holes barrel chambers, but it’s not common. It’s usually only done by a Bubba. There are plenty of good Mk1 barrels available here, if you know where to look. Bubbas just don’t want to pay for one.

Some people claim it can be done safely if the barrel is heat-treated correctly after it’s welded. I don’t think it’s ever really safe.

If you can’t import them, I would make new ones.

[Peter Laidler]

When I was in Australia we had a small programme whereby a round block containing a 7.62mm chamber was pressed into the bored out rear end of a standard .303" barrel so that it became a BFA barrel for the 7.62mm L4's. You COULD try something similar but using a .303" chamber machined down from a scrap No1 rifle barrel. That'd be simplicity itself. But not something I'd bother with..........

Making a new barrel.......... Not something I'd undertake lightly. Far too much a) machining and b) accurate geometrical features involved

[browningautorifle]

I drilled out an MP5 barrel that had been cross drilled and inserted a piece of Sten barrel to replace the damaged part. I then used a chamber ream and re cut the chamber. It worked flawlessly but that's not a Bren chamber is it? I've seen it tried with an M1 carbine once and it didn't work...

[Peter Laidler]

Or just bore out the original butchered barrel in a 1 step down form then line the complete barrel with a suitably machined and sized ex rifle barrel. There's a discussion about the how's, why's and wherefores earlier on this Bren forum. Simplicity itself

[Richard-]

Or just bore out the original butchered barrel in a 1 step down form then line the complete barrel with a suitably machined and sized ex rifle barrel. There's a discussion about the how's, why's and wherefores earlier on this Bren forum. Simplicity itself

Thanks for the replies and feedback everyone.

Peter -thanks for the information re: chamber inserts and barrel re-lining. I remember reading your barrel-lining ideas in one of the other forums.

Vincent - thanks for the feedback. I'm pretty envious of IMA's new Mk 1 barrels for $100 USD but I can't import them unfortunately.

I can get new barrels made by an armorer who has done them before - they are about $2,200 each though, without fittings.

My idea was to tap the hole and insert a threaded plug, with the bottom of the plug contoured to fit the chamber - then weld in place.

I'll put up a drawing shortly.

Cheers,

Richard

[browningautorifle]

Don't thread, just use a milling cutter and cut the old chamber out, set your new stub in and then weld from the sides through the cross hole. Don't use too much heat, try to use TIG if you can. Then recut your chamber...if you use an old piece of rifle barrel, it'll be the right material. It should be a sweat fit. Very tight.

[Joe H]

Richard,

I've never tried to rescue a Bren barrel as they are readily available here in the US. The only thing I can add to the discussion is about welding.

My best guess is that the original barrels are something like a 1035 steel. A Mk 1 barrel drawing (dated Jan. 1950) in Dutch looks like it specified an alloy steel like 4130 or 4140 (see attached pic.). Modern barrels are usually something like 4140. The MkI barrel drawing specified a Brinell hardness of 241-311. Annealed 4140 is around 200 Brinell. This (214-311) is in the Rc range of 22-33. This is typical of the "pre-hardened" 4140 available in the US.

Noting the above I think I would be very careful about welding on the barrel. My experience is that using 4140 rod will give a weld much harder than the barrel material. Any barrel is probably in the medium carbon range so it can be heat treated so I'd want to be careful that welding is not hardening the barrel steel above hardness mentioned above. You don't want a "hard" brittle barrel.The additional hardness above annealed specified was to add a more strength to the barrel.

I think I'd try to keep the heat to a minimum (TIG preferably) and use a low carbon rod.

Doing a little Google translation and converting to Imperial the spec for the barrel is 120,900 psi Tensile & 91,030 psi Yield. Annealed 4140 is 95,000psi Tensile & 60,200psi Yield. They are definitely specifying a heat treated barrel material.

Also just like everything else on the Bren it's probably over-designed by today's standards. I wish I had your situation, a Legal FA Bren, just in need of a barrel. I'd find some way to use that barrel.

Just my 2 cents.

Good Luck

Joe

[browningautorifle]

You don't want a "hard" brittle barrel.

Agreed...the weld was done by a master and it was so tiny it barely showed. Not what the average man would have produced.

[Vincent]

Why can’t you import barrels? Is there a law prohibiting their importation like we have in the US?