My experience with black powder in muzzle loading shotguns is that heavy loads mostly produce more flame beyond the muzzle. With a 14 inch barrel it's just going to be worse.

Folks shooting the Pedersoli reproductions (20 gauge or 50 cal)on another board report significant recoil. Don't know what they are actually loading, but DP recommends 25 grs with a 35 gr max.