Okay, someone shooting as long as I have should know this, but I don't. So to bare my ignorance to all, when someone is describing a used rifle barrel as, "TE of 1.5 and muzzle of .25" what does that mean, and what is the range for a good barrel (this is an M1 barrel if it makes a difference)? A link to a website would be as good as an explanation. I tried a Google search, but kept getting pages with the same kind of description, not a definition.