Winchester NATO-Spec Armed forces Primers forty one are a similar primers Utilized in the Lake Metropolis five.56mm ammunition. These primers are developed to exacting technical specs for shot to shot regularity. All primers are continually and rigorously examined winchester 41 primers for regularity and sensitivity at temperatures and conditions much outside of the range of standard utilization. Winchester assures carefully-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.