Winchester NATO-Spec Armed service Primers 41 are precisely the same primers used in the Lake Metropolis five.56mm ammunition. These primers are constructed to exacting specs for shot to shot regularity. All primers are frequently winchester 41 primers and rigorously tested for consistency and sensitivity at temperatures and problems considerably beyond the array of usual use. Winchester assures carefully-controlled weights of primer mixtures, regularity in size and high quality, precise measurements and tolerances for anvil heights and balance in extremes of temperatures and humidity.