Almost every manufacturer of 1911's like to say they have "match grade" barrels. Okay, but what does that mean? I do not understand what qualifies a barrel as match grade. Obviously it has to do with tight tolerances, but what are they? I have read that Taurus uses an "air guage" to determine theirs, but without defining what that means, it is useless to me. Will some of you please explain what determines if a barrel is match grade or what?