Winchester NATO-Spec Military services Primers 41 are the same primers used in the Lake Metropolis five.56mm ammunition. These primers are built to exacting specs for shot to shot consistency. All primers are frequently and rigorously analyzed for regularity and sensitivity at temperatures and circumstances significantly outside of the range of typical use. Winchester assures diligently-managed weights of primer mixtures, regularity winchester 41 primers in sizing and quality, specific measurements and tolerances for anvil heights and steadiness in extremes of temperatures and humidity.