GEN 2 AR-10 Silent Captured Spring Builder with Alternative Spring PackH2 Buffer VersionIncludes partially assembled SCS unit, three alternative weight springs and spacer to allow for installation in both carbine-length and rifle-length buffer tubes.Recommended Use:Short-barreled rifles (SBRs)Suppressed weaponsRifles recommended to use an H2 bufferSelect-fire riflesPiston-operated riflesCompatibilityThe JPSCS2-10 is designed to work in standard 7-inch M16/M4-length buffer extension tubes on .308 AR-type rifles like the DPMS LR-308. Armalite .308 rifles, likewise, use these standard M16 extension tubes with rifle-length stocks, so this unit will function normally when installed with the supplied spacer. However, Armalite's .308 carbines use a slightly longer, non-standard carbine extension tube. The JPSCS2-10 can still be used with these extension tubes by installing the spacer, which must be modified to fit. Alternately, the system will function readily if the longer Armalite carbine tube is replaced with a standard 7-inch .223 carbine extension tube.The JPSCS2-10 is not compatible with the HK MR762, the Sig Sauer 716, or the Rock River Arms LAR-8 because of its longer bolt stroke and subsequently longer extension tube. It is also not compatible with the POF Revolution DI due to its slightly altered geometry.