Winchester NATO-Spec Military services Primers forty one are precisely the 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 consistently and rigorously examined for regularity and sensitivity at temperatures and conditions much over and above the number of normal usage. winchester 41 primers Winchester guarantees very carefully-controlled weights of primer mixtures, consistency in measurement and excellent, exact measurements and tolerances for anvil heights and security in extremes of temperatures and humidity.