I would use 777 loose powder and start with about 85 grains. Shoot 3-4 times, go to 90 grains and shoot 3-4 times, go to 95 grains............ up to about 110 grains. Use whatever load is most accurate. Remember that loose 777 is 15% more powerful by volume than pyrodex, so an 100 grain load is equivalent to about 115 grains pyrodex.