JP Enterprises EnhancedBolt Bolt Carrier Group BCG 9mm QPQ Finish Short Stroke Heavy SCS System JPSCS2-9SS-5H2 - 2 Tungsten/ 3 Steel Masses Black. New to this revision of our JPBC-9SL and JPBC-9SL-SP bolt assemblies is last round holt open compatibility with our line of short-stroke Silent Captured Springs. This bolt assembly will provide reliable last-round lockback with any compatible receiver such as our GMR-15. Specifications for JP Enterprises EnhancedBolt 9mm AR Bolt Carrier Group (BCG) Kit - JP Short Silent Capture Spring: Manufacturer: JP Enterprises Fabric/Material: 416R Stainless Steel Caliber: 9mm Luger Condition: New Features of JP Enterprises EnhancedBolt 9mm AR Bolt Carrier Group BCG Kit - JP Short Silent Capture Spring Reduced stroke length for faster firing impulse Designed for optimal function with JP Silent Captured Springs for a heavier operating system that reduces bolt bounce while improving reliability and accuracy Tighter firing pin channel to reduce pin wear High-energy tumble process offers a finer cosmetic finish Package Contents: JP Enterprises EnhancedBolt 9mm AR Bolt Carrier Group Kit - JP Short Silent Capture Spring JP Enterprises JPBC-9SL-5H2SS: EnhancedBolt Bolt Carrier Group 9mm QPQ Finish Short Stroke Heavy SCS System JPSCS2-9SS-5H2 - 2 Tungsten/ 3 Steel Masses Black