If your just checking for unsafe chamber dimensions what you need is a field gage. If the bolt closes on a field gage the gun is not safe to shoot. A field gage is the exact maximum safe saami dimension for a given caliber.
To do any gage tests on a ar15 the ejector needs to be removed.
Go gage is the shortest safe saami spec that allows ammunition made to saami maximum spec. field is the longest safe chamber dimension. Go and Nogo gages are typically used when cutting a chamber to spec or setting head space on adjustable rifles like the savage series.
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Last edited by JonM; 02-25-2013 at 01:35 PM.