Your rifle is rated for 150 grains max powder charge. And by no means am I saying shoot 150 grains of powder. There are a number of great powders, loose powders out there that your rifle can shoot. There is BlackHorn 209 which is well liked, then there is Triple Seven which is my favorite, Pyrodex RS another great powder but dirty, and Black Powder. Then there is of course American Pioneer Powder which I shoot but would never hunt with.
Personally I would use 2f Triple Seven Powder. A charge of up to 110 grains is plenty of elk killer power. As for a bullet there are so many now on the market, that to name one, would be unfair. But if elk hunting use a good bullet. The Barnes Copper bullets are good. I like the Barnes Expander but many like the TMZ which I never shot. Parker Extreme are good bullets. Accurate, but I have no experience on game with them. Sabotloader is an elk hunter and owns a couple Omegas. I am sure he can suggest a good bullet and a powder combination for you that will do the job for you. You have a great rifle. Good luck in your hunt.