OK. I have and read a lot of info ( I have THE book) about building SXS rifles out of shotgun actions but they are always building high pressure cartridge rifles. What would be the criteria for building a low pressure bore rifle? I am thinking a 20 bore BLACK POWDER round maybe 70 to 100? grains of FF pushing a one ounce projectile. Would a quality 12 bore action, double underlug lockup with a dolls head, and steel (not Damascus) barrels suffice? I know breech thrust is a concern here also...Your thoughts please, Thanks, Ed