That is more then enough powerfor a deer unless you were shooting some extreme distances. With 80 or 90 grains (I really can not remember) I shot through two deer at 80 yards with a .54 caliber. 70 grains will drop a deer with no problem. Especially with that caliber. The person who introduced me to black powder shooting used to hunt with a CVA Mountain Rifle in .58 caliber. His load was 70 grains and a patched ball. He'd knock the snot out of these big Wisconsin whitetails with that load.

I have one .50 caliber rifle and with 70 grains it is just deadly accurate. The rifle itself is in terrible shape. It was one that was given to me as junk, but I got it shooting. I loan that out to gun poor friends, and almost everyone of them shoots deer with 70 grains and a .490 ball. They have yet to loose one.