Winchester NATO-Spec Military Primers forty one are precisely the same primers Employed in the Lake Metropolis five.56mm ammunition. These primers are developed to exacting specs for shot to shot regularity. All primers are continuously and rigorously tested for consistency and sensitivity at temperatures and conditions much further than the selection of regular usage. Winchester assures carefully-managed weights of primer mixtures, consistency in dimension and top quality, precise measurements and tolerances for winchester 41 primers anvil heights and steadiness in extremes of temperatures and humidity.