5.56×45 NATO Ammunition
5.56×45 ammo derived from the .222 cartridge and was officially adopted as the standardized NATO round in 1963. Essentially, 5.56×45 as a caliber came into being because the military was using 7.62×51 and critics believed the larger round was too powerful for light service rifles, leading to rough recoil and a slower than desired rate of fire in military service rifles. Today, the NATO standard cartridge is designated as “M855”. You’ll often find it in-stock and available to shooters. We also carry a huge in-stock selection of .223 ammo for sale here.
5.56×45 Ammo Types
The majority of 5.56×45 rounds sold today are full metal jacket (FMJ) or full metal jacket boat-tail cartridges. Incredibly fast, with a muzzle velocity that’s generally more than 3,000 feet per second, you’ll find 5.56 ammo with a 62-grain projectile as well as lighter rounds with a common 55-grain bullet. In either case, you can expect muzzle energy to be in the ballpark of 1,300 foot pounds.
.223 Remington vs. 5.56×45 Ammo

While the civilian .223 Remington round is very similar, it is not the same as 5.56×45 ammunition. The two cartridges are loaded to different pressures when adhering to SAAMI (Sporting Arms and Ammunition Manufacturers Institute) specifications. Because of that difference in pressure, you may run into trouble if you elect to fire 5.56x45mm NATO rounds from a chamber with a shorter .223 Rem leade.
Popular Rounds for Sale at  riveraamunition
5.56x45mm is one of the most popular calibers at  riveraamunition While there are a number of reliable rounds, the most popular manufacturers of the NATO round tend to be produced by Lake City, Federal American Eagle, and PMC