I have killed many animals with my 62 caliber (20 bore) flintlock rifle. I can tell you factually, it's been as effective as my 375H&H on anything I have killed, up to a big moose. In fact, I have killed 4 moose in my life, 2 with a 375H&H, one with a Winchester .348 and one with my 62 cal flinter. The only one that dropped at the shot was killed with the 62.
I use 140 grains of 3F powder and a .600" ball
I have killed several deer, 3 elk, 1 moose, and several antelope with it. It's been all I could ask for, within 200 yards.