Winchester NATO-Spec Navy Primers 41 are precisely the same primers Utilized in the Lake Metropolis 5.56mm ammunition. These primers are developed to exacting specs for shot to shot consistency. All primers are continuously and rigorously analyzed for regularity and sensitivity at temperatures and situations far past the choice of usual usage. Winchester assures diligently-controlled weights of winchester 41 primers primer mixtures, regularity in dimensions and excellent, exact measurements and tolerances for anvil heights and steadiness in extremes of temperatures and humidity.