Winchester NATO-Spec Armed service Primers forty one are a similar primers Utilized in the Lake Metropolis five.56mm ammunition. These primers are developed to exacting specifications for shot to shot consistency. All primers winchester 41 primers are continually and rigorously tested for consistency and sensitivity at temperatures and circumstances much further than the selection of typical use. Winchester assures cautiously-controlled weights of primer mixtures, consistency in measurement and high-quality, exact measurements and tolerances for anvil heights and stability in extremes of temperatures and humidity.