wrote:
On Thu, 29 Jan 2015 20:18:01 -0500, Keyser Söze
wrote:

Q. What is the difference between 5.56×45mm and .223 Remington ammo?

*Dimensionally, 5.56 and .223 ammo are identical, though military 5.56
ammo is typically loaded to higher pressures and velocities than
commercial ammo and may, in guns with extremely tight "match" .223
chambers, be unsafe to fire.*

Interesting. When you are talking about 7.62 NOTO and 308, the
opposite is true SAAMI allows higher pressures in the 308 than NATO
allows.

May not be that much difference. Military measures pressure at the neck
and SAAMI measures mid cartridge.