The .223 Remington (.223 Rem) is a cartridge with nearly the same external dimensions as the 5.56 x 45 mm NATO military cartridge. The dimensional specifications of 5.56 NATO and .223 Remington commercial brass cases are identical. The cases tend to have similar case capacity when measured, with variations chiefly due to brand, not 5.56 vs. .223 designation. The result of this is that there is no such thing as “5.56 brass”, or “.223 brass”, the differences in the cartridges lie in pressure ratings and in chamber leade length, not in the shape or thickness of the brass. Drawn from premium American-made brass cups, these casing are rigorously tested to ensure unparalleled durability and dependability, each casing undergoes rigorous in-line and postproduction quality assurance testing to ensure a flawless casing.