I'd look into this Belzona very closely, even to asking the makers how much hoop-stress it will take and explain what you actually want to do with it. Tellignthem the pressures involved are around 30,000 to 35,000PSI, radially, might give them a better idea of what hoop stress there is.

It's machinability is important as after filling the pitts, the chambers will have to be re-cut with a chambering reamer.

It might be the best thing going for old chambers. I personally prefer the thought of having the pits successfully filled, rather than having a liner with in inner joint with silver brazing/solder inside available to pressure and fouling. An almost but not quite perfect joint might be a place for problems to start. An absoltuely perfect joint might be quite difficult.

Reamers are going to have to be purchased either way.

As to getting absltuyely ALL the BP fouling out, that should be accomplised each and every time the gun is cleaned, or they will continue to get deeper.

Water - cold, lots of it flushed up into the tubes, and back out with force - breeches in a bucket. Wet patches might work, but I'd have to see that done successfully - it would take a LOT of patching - flushing is the only way I've been able to get pits clean/clean/clean.

After clenaing some heat applied with dry them perfectly, but do not use really hot water as that will cause soft steels and iron to flash rust as it dries, then sucks moisture out of the air my opinon on why, but the flash rusting is real and is why H&H (THE British Firm) recommends or recommended cold water cleaning to my friend. I've been doing it that way ever since and have never rusted a bore. They've always come out spottlessly clean.

It has been my expierence that cold water cleaning seems to resist the hot water's flash rusting. Indeed, after scrubbing out the tubes, you can set the barrels aside and attend to the locks, before going back and wiping out the tubes.