Needing one of these to check out some used stuff I have now and/or may buy in the future.  Hoping someone can save me a little internet searching.  Thanks.

Brownells has a .223 version.  Would this work with a 5.56 chamber?  Seems like I remember that 5.56 and .223 have different throat profiles and I'm not sure if this will impact how this tool reads.

Bushmaster has a listing for "M16/AR15" headspace gauges on their tool page, but when you click the link to see the actual products they are labeled as .223 gauges.  Since Bushmaster primarily sells military chambered 5.56 rifles and not SAAMI chambered .223 rifles, I wouldn't think they would sell SAAMI gauges but...

Fulton Armory sells headspace gauges as well, including a "G.I. Field Reject" gauge (you have to scroll down or search the page to find it).

You probably will have to call and speak with someone to get the straight story as to exactly what they are selling.


~edited to fix link