Winchester NATO-Spec Armed service Primers forty one are a similar primers used in the Lake Metropolis 5.56mm ammunition. These primers are designed to exacting technical specs for shot to shot consistency. All primers are continually and rigorously examined for regularity and sensitivity at temperatures and disorders far past the winchester 41 primers choice of normal usage. Winchester guarantees cautiously-controlled weights of primer mixtures, consistency in dimension and top quality, exact measurements and tolerances for anvil heights and steadiness in extremes of temperatures and humidity.