FM Products Mike-9 RMB Heavy Buffer 11 oz. Designed specifically for pistol caliber carbines (PCCs) the RMB is a proprietary buffer system that dramatically improves performance accuracy and shooting comfort while maintaining the affordability and reliability that Foxtrot Mike is known for. This RMB Buffer is designed to be used with our VFM-9 Upper Receiver as it is a "Short Stroke" style. If you are building your own PCC upper that is not "Short Stroke" style. you would need an A5 BufFer Tube to ensure bolt lock back. At the core of the RMB is a finely tuned reciprocating mass that eliminates bolt bounce a long-standing issue in traditional blowback-operated PCCs. Combined with a sliding buffer body a dampening spring and a durable urethane impact modifier the RMB system delivers a soft controlled recoil impulse that users will feel immediately and high-speed video testing the RMB with our VFM-9 5 in confirms it: 100percent elimination of bolt bounce. Specifications for FM Products Mike-9 RMB Heavy Buffer: Manufacturer: FM Products Weight: 11 oz Package Contents: FM Products Mike-9 RMB Heavy Buffer FM Products MIKE-9-HB-RMB: Mike-9 RMB Heavy Buffer 11 oz