Drop-in captured-spring recoil system helps your AR function more smoothly and quieter without any permanent modifications. The carefully balanced, custom-ground buffer spring, combined with the JP LMOS buffer, greatly reduces friction and vibration - say goodbye to the annoying “spoon over a cheese grater” noise of conventional springs and buffers. Fits buffer tubes for both M4-style collapsible stocks and also, using the included spacer, the longer tubes for fixed rifle stocks. The Auxiliary Spring Rate Kits for the JP Silent Captured Spring allow custom tuning of the device to a given rifle. While the default spring offers the best performance for the widest range of co Mfg: J P Enterprises SPECS: Stainless steel and hard polymer. 7" OAL. Nylon spacer – 1-5⁄8" long. Instructions included. JPSCS-15 fits AR-15/M16/M4. JPSCS-10 fits AR-style .308 rifles, including DPMS LR-308, ArmaLite® AR-10®. Does not fit Rock River Arms LAR-8.