The Wilson Combat AR9 Optimized Recoil System allows the user to adjust action spring weights to tune their bolts cyclic rate for optimum reliability. This drop-in system is compatible with the Wilson Combat AR9 and similar short-stroke, blowback 9mm AR carbines. The AR9 Optimized Recoil System comes with three full-size 1911 recoil springs (recoil spring weights 15, 17, and 20 pounds) to tune your bolt's speed to optimum reliability. This buffered system will reduce wear and tear on your AR9 and provide you with a softer recoil impulse for faster follow-up shots and is ideal when tuning your gun for competition use. Produced of high-quality, fully hardened stainless steel with no pins or fasteners to fail, the Optimized Recoil System will stand up to years of hard use. The black polymer buffer cushions the action for smoother shooting. (Replace buffers when they become worn or damaged. Extra buffer included.) Comes with 3 recoil springs included to tune to ideal reliability...