I have not had the chance to hunt elk with the muzzleloader yet. As for the powerbelts, I see no reason at all why they would not be able to take an elk. I would use the 348 grain aero tip or bigger because of the penetration you would get with that design. Also they shoot the best out of my rifles.

There are other conicals out there you might want to look at. No Excuse makes 460 grain conicals which do well out of most rifles. There are also some Hornady Great Plains, T/C Maxi Ball, and Colorado Conicals sold at Cabelas.

One thing that a lot of people overlook is the large bore rifles and round ball. Granted you are using a .50 caliber so round ball is not perhaps your best choice.

I have a CVA Staghorn that with 90 grains of Goex FFg and a Powerbelt, I would not even think twice about shooting an elk. I really think this would be an effective load.