A 20 gauge chamber gauge is .685, get or make something of that diameter and stick it in the chamber and see how far it goes in.

Mike

http://www.ebay.com/itm/VERMONT-685-MINUS-PIN-GAGE-AB1562-1-/361425937368?hash=item5426aa23d8:g:FsEAAOSw~bFWPNIi

Last edited by skeettx; 01/07/17 06:57 PM.

USAF RET 1971-95 [Linked Image from jpgbox.com]