Well, all other things being equal (like gun weight, stock design, etc.) I would say my 45/70 may kick about like your muzzleloader would. I have never shot 150 grains of powder out of my muzzlelaoder. I have a 54 cal T/C renegade that I load with 100 gr Pyrodex under a 435 gr maxiball. That kicks about like my 45/70.

With a 45/70, you'll know you've shot a rifle, but it won't make your eyes hurt. If you can hack a .308 or an '06, you'll be fine.