Winchester NATO-Spec Armed forces Primers forty one are a similar primers used in the Lake Metropolis five.56mm ammunition. These primers are designed to exacting specifications for shot to shot consistency. All primers are consistently and rigorously examined for regularity and sensitivity at temperatures and disorders far past the choice of ordinary use. Winchester assures carefully-controlled weights of primer mixtures, regularity in size and high quality, precise measurements and tolerances for anvil heights and stability in extremes winchester 41 primers of temperatures and humidity.