Beretta made a black powder shotgun? Cool. Post a picture of it if you could. I would really like to see it. Is this a muzzleloader or is it just a black powder cartridge type gun? If it is a muzzleloader I would normally say load it like any other 12 gauge black powder shot gun but being an over and under I am not sure that would be safe to do so I will not comment on that. Perhaps you might want to contact Beretta for load information. Good luck with your shotgun.