Maybe. Kinda depends on the amount of reduction and the intended use.
Seeing that stabilizing a bullet is about rpm's ..... a 1:48 twist is a bit lest that 3/4 as long for 1 turn as a 1:66 .... so to get equal rpm's, you neet to drop velocity by about 25%, no?
Not good for deer, as a patched roundball leaves little enough of a blood trail as it is, and is not terribly lethal - it needs every ounce of energy it can get....
I would not be using a Black powder gun on small game- I can use a 4 cent .22lr for that.