The Geissele Super 42 Spring was designed to improve the function and reliability of your AR-15 pattern rifle. Its unique spring design uses three independent strands of wire, just like the German MG42 Machine Gun. This concept acts as a harmonic damper and energy absorber by allowing the springs to flex separately from each other. This flex helps displace excess energy which decreases the chance of spring failure and assists with making your AR-15 more reliable. Compared to the stock spring, The Geissele Super 42 Spring has a decreased tendency to lose length and force over a given round count. As an added bonus, it removes the annoying spring reverberations (twang) heard and felt by the shooter through the buttstock. The Super 42 Spring has a 15% stronger average return force than the standard buffer spring. This will assist in stripping rounds out of the magazine when operating with a dirty weapon or when using steel-case ammo. NOTE: The Super 42 is for use with Carbine length buffer tubes and is not compatible with rifle length or A5 buffer tubes/receiver extensions