Stimpy, If I was you I'd just chamber a 445 super mag in a encore(or contender) barrel and be done. Its a 44 bullet with a 1.600" piece of brass, no trimming or anything, starline makes the brass. 44 mag and special rounds can also be fired through it. Sierra says they can achieve 1800fps out of a 14" barrel and 30.7 grains of 296 powder. Maybe take a 460s&w trim it from 1.790 to 1.600 seat the bullet long and probably keep the same powder capacity and not have to buy a custom barrel. You can also shoot 454 and 45colt through it. I don't think you could ever get the accuracy from a 45-70 chamber with a cartridge as short as you want, that is a long jump for the bullet. My brother had a contender barrel chambered in 45colt/410 and couldn't get it to shoot. Being the pro I am I told him I'd get it to shoot the 45colt accurately , long story short, he traded it for a 30-30. The chamber was too long for the kind of accuracy we knew a contender was capabile of. From what I've read lots of people has this problem with the 45/410, this is what I think you'd run into with a real short 45-70 in a regular 45-70. Dave