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.). Mfg: Sprinco Usa