SPRINCO Reduced Power Buffer Spring - AR-15 Carbine (Yellow)For AR15 .300 BLK or soft cycling guns This is the perfect spring for those soft cycling AR15s that tend to short-stroke and not lock back on an empty mag with a stronger spring. Designed specifically for .300 BLK since they are notorious for cycling very soft, especially with subsonic ammo. Sprinco USA Springs are made from certified Chrome Silicon wire stock to ISO 9001:2008 quality standards to withstand extreme heat and high cyclic rate. This ensures consistency in performance through high round counts. They are precision wound, heat treated, stress relieved and shot peened for extremely long service life and then moly plated for improved corrosion and wear resistance. Expected service life is in excess of 30,000 rounds. Features: Heat Treated Stress Relieved Shot Peened Moly Plated Extremely Long Service Life Compatibility: Soft Cycling AR15 Gas Operated Firearms: This spring is designed specifically for guns that won't cycle reliably with a stronger spring. Designed for the .300 Blackout which is known for cycling soft. This spring is often needed for a .300 BLK to cycle correctly. Also works great for .223 guns that happen to be short stroking and not locking back on an empty magazine.