I bought several items from a gunsmith's estate. One is a pair of barrel blanks, 26-1/2" long, 1.130 OD. Looks like centerfire rifling from the twist. The inside of the muzzles measure .612". That would be the tops of the lands, measuring with a dial caliper. I can do a Cerrosafe cast. What caliber could they have been intended for? The man had built several double rifles.

I also have a pair of 19-1/2" long 22 rimfire barrels, 1.25" OD. Rimfire double rifle? I'll put these and others up for sale as soon as I figure them out.

20 gauge slug would be .615. 600 NE is .620. Or any one of many wildcats.