Plan sounds good, you dont need brass case's with them unless you use BP & I think you still get one shot a case but dont use plastic wads .

Im looking at making 1 or 2 on a Baikal shotgun to use in shotgun only country's or where shotguns are thought to be less dangerous ???

Im eyeing a couple of South American country's

I think more power in 12ga & try RB, in my massive 12bore double rifle I shoot 600gr RB at up to 2000fps, most likely too much in a light shotgun,(my thinking now is 1850fps is the load) but look up some of Ed's 12ga from Hell loads to try !