I have a 180 grain FNGC that does interesting and accurate things from both my Bisley BH x 7.5" and the more recent addition of the steel-frame Henry lever rifle. With a warm load of 14.0 grains of WW-296, the revolver runs at 1350 FPS and hovers around 1700 in the 20" rifle. I think there is safe room for 0.5 to 0.7 grains more fuel, though I derive this from primer appearance and ease of extraction. The powder column has a bit of space left.