RE: need some help
No, you do not have to use 150 grains just because they list them at that and call the "magnum bullets". That is for advertizing for those that buy into the magnum hype. The only thing using 150 grains does in most cases is make the gun kick harder, the deer won't be any deader. It does get your flatter shooting, but for most muzzleloading ranges, that is not an issue.
For example, my load for elk uses 90 to 100 grains of 777 (loose). I can hold dead on out to 120 yards. And that is with a 370 grain T/C maxiball. Sabots would be flatter shooting.