Winchester NATO-Spec Armed service Primers forty one are the exact same primers used in the Lake Metropolis five.56mm ammunition. These primers are built to exacting specs for shot to shot consistency. All primers are frequently and rigorously tested for consistency and sensitivity at temperatures and situations significantly beyond winchester 41 primers the array of usual use. Winchester assures cautiously-controlled weights of primer mixtures, consistency in dimension and good quality, exact measurements and tolerances for anvil heights and security in extremes of temperatures and humidity.