Maxim Defense Industries Heavy Buffer, JP Silent Capture Spring, AR-15, Only Fits Maxim's CQB Stock, Black MXM-47571 This JP Silent Captured Spring System is manufactured exclusively for Maxim Defense to work with the Maxim Defense CQB Stock System only. The JP Silent Captured Spring System requires an open channel in your bolt carrier group assembly for the guide rod to pass during fire. This modified BCG can be acquired from JP Enterprises.