Winchester NATO-Spec Military services Primers 41 are exactly the same primers Utilized in the Lake Metropolis 5.56mm ammunition. These primers are crafted to exacting specifications for shot to shot consistency. All primers are continually and rigorously tested winchester 41 primers for consistency and sensitivity at temperatures and situations much further than the selection of ordinary use. Winchester ensures meticulously-controlled weights of primer mixtures, regularity in dimension and excellent, specific measurements and tolerances for anvil heights and steadiness in extremes of temperatures and humidity.