People and companies have been trying to make a double stack shotshell mag that actualy works reliably for years now. If there was such a thing out there then you would see it being used by the gaming crowd. As has been pointed out already there are some quirks involved when making these things feed from a box. Get your hands on a saiga/vepr 12 mag and take a look at how the guides in the mag help to line up the shells.
Mossberg have come out with a double stack box fed 590 this year so we will have to see how that one progresses.
Good luck in your endevour, you may become a wealthy man if you succeed!
MD Arms Patents Double-Stack Magazines for the Saiga 12 - Guns.com
Bookmarks