Uh, the 45-70 is NOT a muzzle-loader, but either a single-shot cartridge rifle or a multi-shot underlever. Do a little research, eh?
As for the m/e issue, I was under the impression that a 300gr JSP @2530 fps that makes 3678 ft lbs is more than enough.
No doubt the real experts will put me right here.
You'll note that I have, so far, made no mention of muzzleloading...however, you'll all be happy to know that the double rifle BP muzzle-loader is alive and kicking, so to speak. Pedersoli make it in .54 RB and .72 RB.
tac