“RED Spring” EXTRA Power Buffer Spring, Best option for 16″+ 5.56 barrels with carbine length gas system platforms with standard front sight towers and H buffers, 16″ + BBL gas piston guns, *some* suppressed shorties,and later generation Colt LE6920’s, 9mm, 6.8 SPC, 6.5 Grendel, .458 SOCOM, 450 Bushmaster, .500 Beowulf, and assorted “Thumpers” using standard 7″ depth M4 extension tubes. AR-10 Carbines (E.G. Armalite, Noveske, LMT) using deeper extension tubes and standard length carbine buffers to accommodate the longer .308 BCG also use the “RED” Spring. Please call us to discuss successful historical “recipes” for implementation of the RED spring in .308, 6.8 SPC, etc. RIFLE length extension tube platforms. Color Coded RED. NOTE: NOT for use in .308 Carbines using standard 7″ M4 extension tubes and short, stubby buffers.