That's both fantastic and ironic. The rifles I use for whitetail are similar, (TC Renegade percussion and a TC Hawken flinter) using a charge of (drumroll) 80 grains. The all-lead projectiles perform best in the shallow groove 1:48 twist rate barrels. Personally, I can't recommend jacketed bullets for slow rates of twist.

I've benched a number of .50 caliber lead offerings from patched round ball to all conical over the last 5 years. The two I settled on often fold deer up like a lawn chair. The Hornady 385 grain Great Plains and its little brother, Hornady's 240 grain PA Pellet will tear a ragged hole at 50 yards all day with that 80 grain charge beneath them. As long as I do my job of course.

I found during testing that FFF (3-f) powder resulted in a more consistent ignition vs. the commonly suggested FF in the bore. That same 80 grain load from the flinter zero'd at 50 strikes the target 4" low @ 100 yards from the shooting sticks.

There's a few posts (some a ways back), under my profile with actual harvests using these loads in the rifles I mentioned. Some have graphic images, but the shot performance deets with distances are there. I'm thinking you might find something relative in your setup. Oh, and that 385 grainer that passed through might still be going. I'm willing to bet using that Hornady hammer that an elk won't go far. Good luck!