Winchester NATO-Spec Military services Primers 41 are the identical primers used in the Lake Metropolis five.56mm ammunition. These primers are designed to exacting specs for shot to shot regularity. All primers are continually and rigorously examined for regularity and sensitivity at temperatures and circumstances much beyond the winchester 41 primers variety of normal usage. Winchester assures meticulously-controlled weights of primer mixtures, regularity in size and good quality, exact measurements and tolerances for anvil heights and steadiness in extremes of temperatures and humidity.