I've seen that chiappa makes a 12 inch 4570 rifle . I don't know much about the 4570 and barrel lengths but would the 12 inch be too short for propper powder burn or would it be more economical to have a 44 magnum in such a short rifle with almost the same performance? I know the 4570 with longer barrels would be no comparison but we are talking 12 inches here ?
I've thought about this when those Ridge runner rifles came out, and you got me wondering again so I put some numbers into Quick load. I'd be very curious to see what the velocities in an actual 12" rifle would be. The velocities the program spits out for 18.5" barrels are close to what I get with my guide gun so I would tend to believe the short barrel numbers as well.
The following are theoretical maximum loads using IMR 4198 at 40,000 psi.
300 grain jacketed
18.5" barrel 2,185 fps - 3,181 fpe
12" barrel 1,966 fps - 2,575 fpe
350 grain jacketed
18.5" barrel 1,972 fps - 3,023 fpe
12" barrel 1,790 fps - 2,489 fpe
460 grain lead
18.5" barrel 1,681 fps - 2,891 fpe
12" barrel - 1,538 fps - 2,420 fpe
540 grain lead
18.5" barrel 1,492 fps - 2,675 fps
12" barrel 1,378 fps - 2,281 fps
There's definitely some velocity loss when going to the 12" barrel but the above numbers are significantly greater than what can be done with .44 magnum. I get a max of about 1,425 fps with Lee 310 grain cast in my Rossi ranch hand in .44. The 45-70 looks like it can do the same velocity with a 500 grain bullet.