I use Goex FFF black powder, have sighted in at least 10 inlines for my buddies using either the 240 or 300gr Hornady XTPs in .429 caliber and the Harvester plain green sabots...Every one has grouped great with either 80 or 85 grains of powder...I start at 80 and go to 100grs but have always found that sweet spot at 80 or 85grs...