I've spent time in elk camps as both a worker and a paying hunter. I've shot elk and seen elk killed. when elk are not shot correctly, they like to go places that will make you wish you never started this thing. I carried a 338 win mag, but never recommend it to customers, cause most of them couldn't handle it. I carried that rifle all over the west and Alaska. It served me well.
If I was going to hunt elk with a muzzle loader, I'd use a conical or one of the top end bullets we can not speak of here. Today elk hunts for most of us cost a lot of money. On a 5 day hunt you have to take the shot that is offered. If you live in elk habit, you can wait for the shot you want.
I would strongly recommend some PMs to ID Ron and pick his brain. He's done a lot of work with conicals and he has taken a lot of western game with them. I think he knows what the results would be with a lot of combinations you can think of.
Deer are small, you can get away with a smaller gun. when you move up to the big animals, use enough gun, and don't let the key board shooters tell you otherwise. Good luck.