In answer to all who wrote in with concerns about laod markings, I X out any caliber markings on the outside of the barrels on any gun converted, AND I mark the loading info on the barrel flats including powder type and weight and max bullet weight. I make sure that nobody can claim ignorance after the fact. I also do not push the limits of any loading for any converted double rifles. My loads for the 45/70 are well within the strength limits of the gun, about the top end for trapdoor springfields.
My loads for the 20 gauge rifles use the Lyman hour glass shaped slug that comes out at 350 grains using Lyman #2 alloy. I use dead soft lead and that makes them some heavier but not that much. When I proof them, I use a modified base plug in the mold that casts a pure lead slug of 425 grains for proofing only. These are loaded over the same powder charge as the regulation loading. That gives me a projectile that weighs 21.5 % over the service load. Even the proof load bullet is well under and ounce. These are loaded over small amounts of Universal Clays powder to around 1500 FPS. This is not your average dangrous game load but it does great on deer and hogs for sure and would certainly work for black bears as well. Bob H.