Winchester NATO-Spec Navy Primers forty one are the exact same primers used in the Lake City 5.56mm ammunition. These primers are designed to exacting specifications for shot to shot consistency. All primers are continually and rigorously examined for regularity and sensitivity at temperatures and conditions far over and above the number of regular winchester 41 primers usage. Winchester guarantees meticulously-managed weights of primer mixtures, consistency in dimensions and high-quality, specific measurements and tolerances for anvil heights and steadiness in extremes of temperatures and humidity.