Headspace Gage 223 Remington Field
The Field gauge is used to measure the absolute maximum allowable chamber headspace.  The Field gauge is used for a rifle in service that has already passed a GO and NOGO test when built. If the bolt closes on the Field Gauge it is considered unsafe headspace and should be taken out of service for repair.  Excessive headspace will cause more case stretch leading to case failures and a blow-up.  For use in all .223 chambers as well as any 5.56 chamber that is expected to fire any .223 ammo.   This is because .223 ammo is loaded with softer brass or steel cases that cannot handle the case stretch of the longer 5.56 max headspace.  Never fire .223 reloads in a .223 or 5.56 chamber that exceeds .223 headspace specs. The Field gauge is also good to use every 500 to 1000 rounds to detect any headspace problems due to unusual accelerated  wear on the bolt or locking lugs due to improper heat treat of the parts. This gauge ships only in the USA, No export or APO/FPO.