"Last night I fired three shots made up in Brass 12 bore cases, 150 grains of fff black powder, card wad, two felt wads and a 570 grain ball. "

450, I just chronoed some 700gn balls over 145 FFFg last weekend in my 10 and was getting an even 1300fps. I'd imagine your loads are in the 1500-1550 range, which is smokin!!

Keep us posted on your progress.

Bob