I have used this same load in my T/C Black Diamonds with good results. Go up to two pellets, however, and its all over the paper . . . .

Yes, it is roughly equivalent to 79 grains of black powder, and that is plenty.

Well let's see.

The 45/70 BP load, which has killed everything, used 70 grains BP under a 45 cal lead slug. So, 63 gr of T7 has to be good enough.

My 535gr. bullet out of the 45-70 likes 65grs. of black. Deer don't like it. When my brother-in-law was shooting his .50 double barrel...he used 50grs. of black behind a patched roundball. I've seen the deer he shot with that load...they were just as dead as mine. That 63 oughta do.

It seems we have consensus more or less. 63 gr is plenty, especially if it is 777, which is hotter than BP. Does your gun and projectile like it though, that is the question. Tight groups are what you look for. I can say from my experience that my groups are super at low charges of 777. Now, is it because I am less likely to tense up when I know there is a light charge in the gun? I am definetly steadier and more relaxed when I know I am not going to get THUMPED when I touch her off. Shooting is much more fun with plinking sized loads, out of my flinter. I have shot in the same hole quite a few times at 50 yards with 40 gr of 777, Never with 80 gr. I don't claim to hunt with 40 gr. but 63 gr. would do for whitetails, IMO. I might even try 63 gr. at the range next time, to see how it goes.

Well, 60 grains of FFg was the standard service charge used with the Minie ball in the Springfield rifle-musket during the Civil War. This piddling charge pushed a 530-grain Minie ball fast enough to kill MEN out to 400+ yards! So tell me that a charge of 777 equivalent to 70 grains of FFg won't push a 320 grain .50 cal. bullet fast enough to kill a deer if the bullet is properly placed? NUTS!!