Geno:
I agree that a slow shotgun powder like Blue Dot may be well-suited to 'bore' rifles such as the 8, 10, and 12-bore guns, especially with round balls at 1000 to 1250 fps. With the larger conicals at slightly higher velocities, however, I would prefer slower powders, in the 'rifle' range. For the .577, definitely rifle powders IMHO.
In my experience, powders like ADI's AR2208 (sold in the US as Hodgdon's 'Varget')will burn completely in a 26 or 28-inch barrel while pushing a 650gr Woodleigh to 1650 fps. In a 22-inch barrel, there is evidence of partially-burnt powder kernels in the bore. In that rifle, I use AR2206, which is ADI's next fastest powder but still in the 'medium' range, and no partially-burnt powder remains in the bore.
I should add that using AR2208 (Varget) in the short barrels works fine regarding accuracy and ballistics, but the muzzle-blast is spectacular so obviously a slightly faster powder was required for optimum efficiency.
Hope this helps.
