Winchester NATO-Spec Armed forces Primers forty one are a similar primers Utilized in the Lake Metropolis five.56mm ammunition. These primers are built to exacting specs for shot to shot consistency. All primers are winchester 41 primers regularly and rigorously analyzed for regularity and sensitivity at temperatures and circumstances much over and above the choice of normal usage. Winchester guarantees cautiously-controlled weights of primer mixtures, regularity in size and high quality, precise measurements and tolerances for anvil heights and stability in extremes of temperatures and humidity.