Cartridge Dimensions
The 5.56×45mm NATO has 1.85 ml (28.5 grains H2O) cartridge case capacity.
5.56×45mm NATO maximum NATO cartridge dimensions. All sizes in millimeters (mm).
Americans would define the shoulder angle at alpha/2 = 23 degrees. The common rifling twist rate for this cartridge is 178 mm (1 in 7 in) or 229 mm (1 in 9 in), 6 grooves, Ø lands = 5.56 mm, Ø grooves = 5.69 mm, land width = 1.88 mm and the primer type is small rifle.
According to the official NATO proofing guidelines the 5.56×45mm NATO case can handle up to 430 MPa (62,000 psi) piezo service pressure. In NATO regulated organizations every rifle cartridge combo has to be proofed at 125% of this maximum pressure to certify for service issue. This is equal to the C.I.P. maximum pressure guideline for the .223 Remington cartridge, that is the 5.56×45mm NATO parent cartridge.
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