Quote Originally Posted by MZ5 View Post
Uh... what? Where are you getting this from? I'm looking at all 3 case (SAAMI's 223 Rem, CIP's 223 Rem, and NATO's 5.56x45mm) drawings and these dimensions are identical. Same body diameter at both the 'base' (web immediately forward of the extractor groove) and the shoulder, same head-to-shoulder length, and same case head diameter. There is the allowance for a 0.001" diameter difference across the diameter of the tapered end/face of the rim, which has nothing to do with either the size, capacity, nor taper of the case.

Now, if you're using that reamer dimension diagram to try to extrapolate brass/cartridge dimensions, then I can see where you might make incorrect assumptions. However, to reiterate for clarity: Cartridge dimensions are identical.
This $hit is getting old, the chamber was enlarged and chrome plated to prevent jamming starting in 1967.