Strike SIAR10FWS AR10 Flat Wire Spring 17-7 Stainless Steel 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. Type: Recoil Spring Model: AR-10 Material: 17-7 Stainless Steel Finish: Stainless