The KynSHOT RB5000L Recoil Buffer is a hydraulic buffer system designed and optimized for softer cycling, under gassed AR-15's using a Mil-Spec style carbine buffer tube (7" internal depth). The RB5000L can be paired with any style buffer spring, however in most cases, the buffer pairs best with reduced powered springs. This buffer is intended to be used with AR-15's that wont lock back on the last round with standard AR-15 buffer system or a heavy buffer. The RB5000L's unique design is made lighter and requires less force to cycle than Kynshot's standard AR-15 buffer system, which is perfect for low velocity ammunition like the .300BLK. Please note, .300 BLK applications exclusively running supersonic ammo can use our standard AR-15 buffer system if the bolt cycles firmly and has proper ejection placement.