WOW, there is a bunch of good stuff to talk about here...
First, I don't like the way those gauges are rebated all the way around.
You are slightly reducing the ability to measure across the whole bolt face like the cartridge case does.
Dave manson does a better job, he just grinds a simple slot on one side where the ejector will fit.
I have a surface grinder and I can do this modification for $5 per gauge if anyone else wants their gauges cut.
Next to Mongo's question:
> I need clarification on this issue. Do .223 gauges measure to the same place on the chamber shoulder as the 5.56 does? If I understand it correctly, the chamber differences are in the throat, lead angle, etc.
The 5.56 and the 223 both use the same datum line.
The datum line, for those not familiar, is a specific diameter on the shoulder.
In the case of 223/5.56, it is 0.330" on all the similar cases such as 221, 222 and 222mag.
What this means is that if you were to scribe a line on the gauge shoulder exactly where the shoulder is 0.330" in diameter and then measure to the end of the gauge, you SHOULD get the dimension marked on the gauge.
The major difference between 223 and 5.56 is in the field reject length and in throat dimensions.
Reference these:
Reamer dimensions:
www.ar15barrels.com/data/223-556.pdfHeadspace gauge dimensions:
www.ar15barrels.com/data/headspace.pdfRandall Rausch
www.ar15barrels.com