He was talking either about a throat erosion gauge or a muzzle wear gauge.
If the rifle in question is a civilian bolt action, I doubt very much that it has seen enough use to even bother checking with either gauge. It takes thousands of rounds to begin to show enough throat erosion to affect accuracy, and muzzle wear is usually caused by cleaning from the muzzle (common with M1 and M14/M1A rifles), seldom done with bolt actions, which are normally cleaned from the breech.
No harm in checking, of course, but I would not expect much in the way of revelations.
(BTW, a TE gauge is set up for a specific rifle and depends on the configuration of the receiver for a reference point. If he has a TE gauge for, say, an M1 rifle, it won't work for, say, a Remington 700.)