Standard Power Buffer Spring. Equivalent spring load to a brand new Mil-Spec M4 Carbine Spring. This spring will perform reliably in any properly configured and maintained 5.56 Carbine if you wish to maintain the performance of a "fresh" Mil-Spec load spring without concern for replacement. This is the best choice for shooters and purists that wish to maintain the performance of most factory supplied new Mil-Spec springs, but do not wish to be concerned with frequent replacement of same or do not have the time or inclination to seek enhanced performance options. Just consider it as permanent new Mil-Spec spring.