Hey, Hale. I' m shooting 90 grains of Pyrodex P in my Traditions .50 Lightning lightweight with Powerbelt 295-grain bullets, and it shoots pretty tight at 100 yards. I think your choice of a 400+ grain Powerbelt will be great. Start with 80 grains and work up. 777 is about 20% more powerful than Pyrodex! As you know, in CO you have to use a full bore-size bullet. I think sabots suck!!

BTW, there' s nothing wrong with shooting an elk with your flintlock, if it shoots better for you!!!