Developed in 1980 by FN Herstal, the 5.56x45mm NATO cartridge has been the standardized round for the US military and NATO allies for decades. The round is perhaps the most popular centerfire round in North America thanks to the proliferation of the AR-15 semi-automatic rifle in addition to other rifles like the Ruger Mini-14, Tavor, SCAR 16S, and Kel-Tec RFB.
Continue History of PMC 5.56 Ammo here: https://ammo.com/brands/pmc-ammo/pmc-556-ammo#caliber-history