I was just noticing that the muzzle gage does not really read the muzzle erosion, so much as it reads the FIRST tight point at the end of the bore that stops the insertion of the muzzle gage.

The muzzle gage actually reads from .297-.304

I have a barrel I counterbored on the lathe with a 5/16" bit, 1/2" deep. Yet despite the .312 hole, the muzzle gage reads a zero on the gage. The reason is the gage is encountering a .297 bore at the 1/2" deep point, while the muzzle remains .312, and will not go deeper.

I have a new Fal bbl right here and the bore will not accept the gage at all, idicating a bore tighter than .297, the smallest dia the gage will read.

I have a SA 3-44 bbl here that clearly reads a "one", but the muzzle is likely a "2", as I can almost rattle the gage a bit.

So my point is that only a pin gage set, say from .296 -.305 can accurately read the actual muzzle erosion at the end. You would take each pin gage and read the one that will not go in as the muzzle size.
I believe that the bore size, while nominally a .300 is actually tighter at around a .297 or so.

Anybody else notice this?
Information
Warning: This is a relatively older thread
This discussion is older than 360 days. Some information contained in it may no longer be current.