Gregg--I would say the barrel would have to be about
1.8 inches in diameter at breech to take higher pressures.
So you could work from that to scale a break action.
I would do it monoblock style so all he has to do is barrel and you screw it into the monoblock.Have threads 1.5 in.
Now if you don't want to build action, you could get a
BORCHARDT FALLING BLOCK. They are big enough.
Cut rifling is fine and it is easier to do.Example-For a 1 inch bore if using jacketed bullets, you need .012 rifling I think, so the land diameter
would be .988...Sounds like a great deal, as your friend
will get more work than he needs.Ed.