Repairing Bren Mk 1 barrel

[Peter Laidler]

It would HAVE to be reduced I'd say. I know some will say '......but you're reducing the amount of meat on the bone.....' but I say no. You've still got the same amount of meat but in two different forms. The insert and the original barrel. Both of which are a known quality steel. You can call it an insert or anything really but it just a bushing subject to an internal loading and there's plenty of examples to take on board.

But a great project for a undergrad students I'd say..........

[Richard-]

What if the insert was reduced slightly in diameter, and then threaded in, and secured with silver solder?

Between the thin cylinder walls and the barrel heating up when fired, I'm concerned I won't get enough adhesion with a shrink fit.

As long as the chamber insert has enough wall thickness to withstand a .303 proof load with a safety factor, it shouldn't require the exterior of the existing barrel to provide strength.

[browningautorifle]

threaded in

Harder to do than you can imagine. I've done them with just a barrel stub from .303 and then swage fit into the barrel. The machining was tight. The barrel had a hole drilled right through so I had a tig spot to hold it in place. The stub of barrel was completely submerged though. Not stuck out.

[Richard-]

Thanks for that browningautorifle, I'm thinking that will be the way to go for this barrel.

If I make the insert over-length, I can mill some flats on it, then machine that part off.

What thread pitch and insert diameter did you use for your repair?

[Joe H]

BAR,

Were you working on a .303 Bren barrel? Can you provide a little more detail or a sketch?

Thanks,

Joe

[Peter Laidler]

It looks to me Richard that you doubt your own ability to bore the barrel and machine the insert to fit. All you need is what engineers call a '....stonking good fit'. It needs to be a tight fit when cold and a drop-it-in fit when hot. Nothing else. That should be simplicity itself for a good quality machinist. I can assure you that there's nothing to feel guilty about to ask a better machinist to do a precision job.

As for threading the insert in, remember this. Threaded in is good when it's under tension but once you have threaded the part you have reduced its external diameter and radial strength (oh yes you have.....) AND reduced the wall diameter diameter of the original barrel too. Food for thought.

[browningautorifle]

What thread pitch

I didn't thread. Get off that idea, mine was just a press fit.

Were you working on a .303 Bren barrel?

I've worked on several this way. I only had one Mk1/2 Bren I didn't want to get into it because there are several of us here that are less than enthused about restoring a hi pressure cartridge this way... There were holes on each side of the chamber as it was drilled through. I made the insert from a piece of #4 rifle barrel and then tacked it in through the holes, a VERY skilled man with TIG did the work. Almost invisible and almost no discoloration...machined off to correct and chambered...tested and was correct. The outside holes remained and the barrel held the pressures. It will never be exposed to extremes of firing again though so who knows? No sketch required. Just use and end cut mill and run it in to the depth of the cartridge shoulders as Peter has instructed. Then machine your barrel section to fit sweat tight. Chill the insert and heat the barrel shank. Tap in place and cool...I TIG welded to avoid embarrassment. Chamber to taste and get to work.

I say all this knowing there are vastly more qualified here watching what I write...now at 77 posts and we still haven't this sorted out.

[Joe H]

Thanks Jim,

An actual demill that was fired

I was leaning toward the threading idea but with BAR's and Peter's experience. I'm now thinking a .65" dia sleeve shrunk in with about .0005- .001" interference. That would give 1/8" walls in the .9" (23mm) area. This should give adequate adhesion. After doing a little figuring I don't think Richard's sketch would give adequate adhesion to the sleeve. I think you need the full 51mm. Tightly thread the demill hole with a plug and tig at the OD first so that the machining for the sleeve will give a good fit between the plug and sleeve. Chamber and fit the end contour after fitting the sleeve.

My thoughts,

Joe

[Flying10uk]

Richard, how about doing a revised drawing for us to look at, similar to the one you provided previously, incorporating the various modifications/improvements which you have now decided on?

[browningautorifle]

An actual demill that was fired

More than one my brother...yes.