Hey y'all. I want to take my browning bps10 and mount it under a ar15. With a 19" barrel to the back of the action its 28" . A 3" 12 ga with 19" is 26.5" overall to the action. I see that usually a m203 mount is used. How does that part mount to a shotgun? Drilled & tapped? . Probably mount it on a rifle not carbine sinse it would be kinda long. Oh yeah the bps 10 ga is a 4+1 capacity don't know what they usually use for 12 ga masterkey