Winchester NATO-Spec Army Primers 41 are the same primers Employed in the Lake Metropolis 5.56mm ammunition. These primers are created to exacting technical specs for shot to shot regularity. All primers are continuously and rigorously tested for consistency and sensitivity at temperatures and ailments considerably further than the selection of typical usage. Winchester assures carefully-managed weights of primer mixtures, winchester 41 primers consistency in dimension and excellent, precise measurements and tolerances for anvil heights and balance in extremes of temperatures and humidity.