Winchester NATO-Spec Navy Primers forty one are the exact same primers Utilized in the Lake City five.56mm ammunition. These primers are built to exacting technical specs for shot to shot consistency. All primers are continually and rigorously winchester 41 primers tested for consistency and sensitivity at temperatures and circumstances far outside of the choice of typical usage. Winchester ensures cautiously-controlled weights of primer mixtures, consistency in sizing and good quality, specific measurements and tolerances for anvil heights and stability in extremes of temperatures and humidity.