If sabots can be used in Nevada, you might be further ahead to shoot a quality sabot out of your Knight Rifle instead of a powerbelt. Knight rifles are known for their long range hard hitting ability shooting sabots. What model of Knight Rifle did you purchase? Are scopes allowed in this area? What are the muzzleloading rifle restrictions.. some places do not allow in line rifles?

I think you're wise in starting with 100 grains of powder and working up a load from there. Personally I would use loose Triple Se7en powder with a 209 primer ignition system. A once in a life time elk hunt would deserve a once in a life time sure shot with the rifle I was going to carry. Just because of the chance you might have to shoot further then 100 yards you can then start building on your projectile and powder charge until you have pushed that projectile to the limit of its best possible accuracy.

I think I would group an inch high at 100 yards. Then you should still be very close at 125 yards and even further depending on the point of aim in the kill zone of the elk. Good luck with your elk hunt. It does sound exciting and I envy you for your opportunity..