As Cayquad said eye reliefis important since I use mag loads [to me they seem to be the most accurate] I prefer at least 4 and go for 5 inches when I can get it.
The main differance in shot gun and muzzle loader scopes is where the parrelax is set for an inline that is capable of 1 to 2 inch groups at 100yds I would get a regular rifle scope with the parrelax set at 100yds. A 1.5 x4 power or a 2 x 7 poweris excellant for hunting and will do well enough for target shooting.Lee