...you can use any mag you want.
(1) Frames, receivers, receiver castings, forgings or
stampings
(2) Barrels
(3) Mounting blocks (trunions)
(4)*Muzzle attachments
(5) Bolts
(6) Bolt carriers
(7) Gas pistons
(8) Triggers
(9) Hammers
(10) Disconnectors
(11) Buttstocks
(12) Pistol...