Sep 6, 2015 #71 RunnerRunner Active Member Nov 15, 2013 292 16 Renegade said: This needs a special BCG slotted for Glock Mags? Click to expand... There are two versions of 9mm BCGS being made right now. Colt 9mm BCGs, and Glock Mag 9mm BCGs. You just have to get the correct BCG--just like buying the correct bolt for a different caliber for an AR-15.