Both the cartridge and chamber are specified in the SAAMI prints.

You can see there the 5.56/223 chamber headspace min dimension is 1.4636 +.010

The Cartridge headspace dimension is 1.4666 -.007

A little careful math will reveal that for most cartridges, there is potentially .003 of "crush" built into the design.

In other words, the max cartridge is .003 longer than the min chamber.

Although this seems fundamentally wrong for an autoloader, in practice, most factory ammo is made toward the minimum spec of .007 shorter, which provides .004 of clearance rather than .003 of interference.

The short version of all that is, yes the min/max values are right in the prints.



Quote Originally Posted by triggerjerk View Post
I think I understand the guages and their headspace measurement along with measuring of fired cases to get an idea of individual chamber headspace. Admittedly my googiefie is suspect, and I haven't spent much time looking, but on the unfired ammo itself, I cannot find "headspace" max/mins. Just distance of shoulder breaks from the base.

Would someone please straighten me out and educate me as to the minimum headspace for unfired 223 and for 556 ammo? Thanks