Never heard of different gauges. Go/no-go gauges measure only headspace or cartridge base to shoulder datum. As the standard measurements in SAAMI/CIP diagrams show lengths of base to shoulder, base to neck, and shoulder angle to be the same between the cartridges, the length to datum should be the same too. Others may have better information, but I don' t recall that the description of a "looser" chamber for 5.56 x 45 means a longer case body, rather a potentially slightly wider chamber and a longer throat due to a different leade angle. So, I don't think the go/no-go gauges would be different?Has anyone heard of a set of no-go gauges for .223 vs 5.56mm? I imagine that commercial barrel makers use the same reamer for both. Would some shop actually change reamers when making an AR-i5 vs bolt action gun?
If there are any barrel makers out there, please chime in.