Winchester NATO-Spec Army Primers 41 are exactly the same primers used in the Lake Metropolis five.56mm ammunition. These primers are designed to exacting specs for shot to shot regularity. All primers are continually and rigorously analyzed for winchester 41 primers regularity and sensitivity at temperatures and ailments far outside of the choice of typical utilization. Winchester assures cautiously-controlled weights of primer mixtures, consistency in size and good quality, exact measurements and tolerances for anvil heights and security in extremes of temperatures and humidity.