Stern Defense makes great AR magazine well adapters which turn your AR Lower into a Pistol Caliber Carbine. There are several models available which accept Glock magazines (9mm/.40), Beretta magazines (9mm) and two S&W M&P magazine versions in (9mm/.40 and .45 ACP). The latest version, the MAG-ADMP9&40/P320 , uses both SIG P320 magazines and S&W […] Source