The SI Flatwire Spring for is an economical, easy upgrade to any .308 AR system. The flatwire spring increases service life of the platform, smooths out the shooting cycle, and greatly outlasts the stock spring. Increased bolt load, in addition to decreased compressing force increases reliability in cycling.The SI Flatwire Spring is an economical, and easy upgrade to any 308 AR system. The flatwire spring increases service life of the platform, smooths out the shooting cycle, and greatly outlasts the stock spring. Increased bolt load, in addition to decreased compressing force increases reliability in cycling. Additionally, all SI Flatwire springs are cryogenically cycled to provide greater consistency, longer spring life, and greater resilience to high cyclic rates. At a cost not much greater than stock carbine springs, the SI Flatwire is an easy option for those either looking to replace worn buffer springs or begin new builds. Features: Cryo-cycled chrome-silicon steel for strength, reliability and longevity Decreased harmonics lessens system vibration for faster follow up shots No more AR twang Compatible with all standard AR10/SR25 receiver extension lengths