Winchester NATO-Spec Navy Primers 41 are the same primers used in the Lake Town five.56mm ammunition. These primers are designed to exacting requirements for shot to shot consistency. All primers are continually and rigorously tested for regularity and sensitivity at winchester 41 primers temperatures and problems much beyond the range of ordinary utilization. Winchester assures thoroughly-controlled weights of primer mixtures, regularity in size and high-quality, precise measurements and tolerances for anvil heights and steadiness in extremes of temperatures and humidity.