Winchester NATO-Spec Armed service Primers forty one are a similar primers Utilized in the Lake Metropolis five.56mm ammunition. These primers are built to exacting specs for shot to shot regularity. All primers are frequently and rigorously examined for regularity and sensitivity at temperatures and problems considerably past the range of standard use. Winchester assures very carefully-controlled weights of primer mixtures, consistency in measurement and high winchester 41 primers quality, precise measurements and tolerances for anvil heights and balance in extremes of temperatures and humidity.