Winchester NATO-Spec Military Primers 41 are the same primers used in the Lake Town five.56mm ammunition. These primers are built to exacting specifications for shot to shot regularity. All primers are constantly and rigorously analyzed for consistency and sensitivity at temperatures and problems much over and above the variety of standard usage. Winchester assures diligently-controlled weights of primer mixtures, regularity in dimensions and good quality, precise winchester 41 primers measurements and tolerances for anvil heights and security in extremes of temperatures and humidity.