SPRINCO USA M4 CARBINE CS SPRING KIT

Extra Extra Power Buffer Spring. The Orange spring is much stouter than the Red spring. The Orange buffer spring was originally engineered for the demands presented by .308 / 6.5 CM / .260 Rem, etc., heavy BCG carbine DPMS Pattern applications using standard 7" Depth M4 extension tubes and short 2.5" buffers (Including aftermarket "heavy buffers") in robustly gassed 16” - 18” ML gas carbine platforms, but has been proven to be a requirement for tuning over gassed carbines of any equivalent heavy calibers in AR-10 pattern tubes with 3.25" buffers or lesser calibers (5.56, etc.).