The Foxtrot Mike Products FM-9 Heavy P.C.C.Buffer Kit includes a proper P.C.C. Recoil spring, guaranteeing optimal feeding and reliability of a 9mm P.C.C.The 6.4oz Heavy Buffer is the perfect weight to ensure reliable feeding of any blow-back operated P.C.C. 3.7 inch overall length, requires no spacer and helps prevent bolt catch breakage. Smoother function, less felt recoil, and reduced rate of fire from your AR pistol.FM Products uses a Premium .308 Carbine Recoil Spring to soak up the recoil impulse created by Blow Back platforms. The extra heavy duty recoil spring helps with feeding and reliability, and is critical to reliable function of a 9mm Blow Back gun. Compatible with all blow-back 9mm upper receivers; Salt bath Nitride Melonite/QPQ finish gives lubricity and wear-resistance; Heavy 6.4 oz. (pistol) weight Comes with a .308 Carbine Recoil Spring to ensure proper function of your 9mm P.C.C. Build