"Purpose-built for 9mm AR-15 pistol caliber carbines, our Generation 2 PCC blow-back carriers keep the features of our well-loved first BCG with modern improvements.  We maintain the dual COLT/GLOCK compatible geometry, user-removable weight and full-auto compatibility while adding new and welcome features. We maintain a ""ramped"" bottom so any common trigger can be used - ideal for competitive shooters and plinkers alike.  The extractor has been upgraded from an internal ""1911"" style claw to an AR-15 pivoted and sprung option. For ease of disassembly, a standard firing pin cotter pin is used, and to ensure long-life, the carrier key is separate from the charging surface ensuring that the carrier stands up to any vigorous action - no sheared keys! A stronger firing pin rounds out the new changes.  Technical Specifications Carrier & Integrated Key: Compatibility: GLOCK & COLT - Style Lower Receivers Carrier: MIL-SPEC 8620 Steel Material Fully Heat Treated External M-16 Style Extractor M16 (FULL-AUTO) Compatible Salt Bath Nitrided Dust Cover Compatible Weight: 14.9 Ounces Removable Carrier Weight - Compatible with JP Enterprises and similar buffer systems. Compatible with MP5 magazine lower receivers Tech Note- Faxon's 9mm BCG is not compatible with Spike's Tactical Colt 9mm lower receivers."