hi, i own an 1874 rolling block which has been converted to 28 gauge shotgun caliber. the barrel has straight rifling.

can anyone give me some information about this type of shotgun? i can only find information on internet about the normal 12,17 and 12,7mm rifles but not the shotgun.

i would like to use it to shoot lead bullets in brass 28 gauge magtech shells.

does anyone know what the diameter of the barrel is?

someone i know suggested i should put the lead bullet inside a plastic shotcup and make the cartriges like shotgun cartridges, but i would like to know if i can use a bullet direct in the brass cartridge (either paper patched, or a bullet with grease grooves)

sofar i have only found 1 information about powder/load. it says 1.5 or 2 drams of FFg black powder, and 3/4 ounce of shot.

ofcourse it is not easy to find a bullet that is 3/4 ounce, so how do i find out the right amount of black powder for a bullet.

i tried calculating it using the "equal volume loads", taking into account that 1/2 of the volume of shot is air, and 1/2 of the volume is lead. is it correct to calculate blackpowder loads like this?

i hope someone can give me some information or point me where i can find information, as no one i know has knowledge of blackpowder guns/shotguns/rifles