What part of colorado are you hunting? What muzzleloader?

The reason i ask is due to different terrain the elk are in and if you plan on doing shoulder shots, which i advise you not to do, you'll want a good blood trail. But for elk i'd use either the 350 grain TC maxi hunter or the 385 grain great plains bullets. Both are excellent bullets. 90-100 grains of powder will be more than enough. Just get a good solid Lung shot and you'll find an elk down when the smoke clears.