NEW FRONTIER BOLT CARRIER AR-9 9MM BLACKNEW FRONTIER BOLT CARRIER AR 9 9MM BLACK FEATURES Caliber: 9mm Glock & Colt Compatible **NOTE: Many Aftermarket drop in triggers use modified hammers which may not reset properly, or hit the firing pin square on the carrier which could cause firing pins to bind and snap. We recommend using only MILSPEC hammers with any 9mm, . 40, or . 45 blowback bolt carrier groups. **A small amount of Loctite is recommended on the set screw that holds the BCG weight