Winchester NATO-Spec Military Primers 41 are precisely the same primers used in the Lake City 5.56mm ammunition. These primers are built to exacting specs for shot to shot regularity. All primers are constantly and rigorously tested for consistency and sensitivity at temperatures and ailments far past the choice winchester 41 primers of regular usage. Winchester guarantees meticulously-managed weights of primer mixtures, regularity in dimensions and high-quality, specific measurements and tolerances for anvil heights and stability in extremes of temperatures and humidity.