Winchester NATO-Spec Military services Primers forty one are a similar primers used in the Lake City 5.56mm ammunition. These primers are designed to exacting specifications for shot to shot consistency. All primers are consistently and rigorously examined for regularity and sensitivity at temperatures and disorders far over and above the choice of normal use. Winchester assures cautiously-controlled weights of primer mixtures, regularity in size and high quality, precise measurements and tolerances winchester 41 primers for anvil heights and stability in extremes of temperatures and humidity.