Winchester NATO-Spec Navy Primers forty one are a similar primers used in the Lake Metropolis 5.56mm 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 outside of the range of regular usage. Winchester guarantees meticulously-controlled weights of primer mixtures, consistency in measurement and excellent, specific measurements and tolerances for anvil heights and security in winchester 41 primers extremes of temperatures and humidity.