I have never hunted elk with a muzzle loader. But if I had to I would look for a heavy bullet, 300 grain or better. Then I would push that as hard as accuracy would allow. In the bullet design I would look for penetration, and then expansion as uniform as possible. So I would look at Barnes, nosler, shockwaves, or even a big heavy conical. I don't shoot an omega but I do have a black diamond. I do know someone with an identical rifle to mine took a elk with 110 grains of triple seven and a 375 grain all lead buffalo bullet ssb.

If I were hunting tomorrow, it would be shooting a 500 grain all lead conical bullet and 100 grains of triple seven out of my White rifle. Good luck with your hunt.