Winchester NATO-Spec Armed forces Primers forty one are the exact same primers used in the Lake Metropolis five.56mm ammunition. These primers are developed to exacting technical specs for shot to shot consistency. All primers are consistently and rigorously analyzed for regularity and sensitivity at temperatures and circumstances significantly beyond the variety of ordinary usage. Winchester guarantees very carefully-controlled weights of primer mixtures, consistency in dimensions and high-quality, winchester 41 primers specific measurements and tolerances for anvil heights and stability in extremes of temperatures and humidity.