Winchester NATO-Spec Armed service Primers forty one are a similar primers used in the Lake Metropolis five.56mm ammunition. These primers are built to exacting specs for shot to shot consistency. All primers are regularly and rigorously analyzed for regularity and sensitivity at temperatures and circumstances much over and above the number of regular winchester 41 primers utilization. Winchester ensures meticulously-managed weights of primer mixtures, consistency in measurement and excellent, specific measurements and tolerances for anvil heights and steadiness in extremes of temperatures and humidity.