This is a subject that has been debated about and written about here before . I got a new upper from Guns-R-Us . All mil spec . The bolt would close on a 223 rem no go gauge but not on a 5.56 gauge . The bbl was refitted to the bbl ext. to 223 spec. So there is a difference.
I know some are asking why ? Because this upper will see mostly 223 reloads and a 223 reloading die set will be used . With a 223 chamber brass should last longer I hope. It still chambers 55 gr 5.56 ammo , have not tried weighter options .
Anyway just wanted to share what I found .
Brownell's sells both no go gauges but only list one Go gauge , more speculation ................
