Winchester NATO-Spec Army Primers 41 are the same primers used in the Lake Metropolis five.56mm ammunition. These primers are designed to exacting technical specs for shot to shot regularity. All primers are consistently and rigorously tested for consistency and sensitivity at temperatures and disorders much further than the variety of normal usage. Winchester guarantees very carefully-controlled weights of primer mixtures, regularity in sizing and high-quality, exact measurements winchester 41 primers and tolerances for anvil heights and stability in extremes of temperatures and humidity.