This is a new B&T USW320 grip shell for a P320 fire control unit. This will work on fire control units from a 9mm, .357 SIG, or .40 S&W pistol only. If P320 is chambered in .45 ACP this WILL NOT WORK with your fire control unit. The removable stock is included and all NFA rules apply with the stock attached. These will only accept FULLSIZE magazines and preferably the Gen2 mags. The Gen1 mags will seat in the USW 320 but it takes some force and we cannot guarantee reliability with these mags. The difference between the "Gen1" and "Gen2" mags is the updated base plate. Compact and Sub-Compact magazines will not work. Does not work with Italian magazines.