Hi, all.

In a fit of boredom I decided to attack my No. 4 Mk. 1 (T) with my set of plug gages. (Or gauges. But the mfr calls them gages).

Peter Laidlericon, in his book "The Armourer's Perspective," writes (p. 91 ff)
"The barrel can be gauged in the following manner. After thorough cleaning, a .301-in. diameter gauge, 2-in. long, must pass cleanly through the bore... A gauge of .307-in. must not enter the muzzle by more than 1/4-in."

OK. Done. I didn't drop it all the way through but the .301" is a slip fit, and the .302 won't even start.

So far, so good.

Now to the chamber end.

Again Peter Laidler:
"To test the lead from the chamber to the rifling, a sure test of a shot-out barrel, a .308-in. gauge must not enter the barrel more than 2.5-in. This distance of course includes the length of the chamber into the lead."

I don't understand where the "zero" of this 2.5 inches is. Is it from the breech face? The bolt face? Something else?

Thanks.
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