“AIR-GAUGED” PREMIUM BARREL DOUGLAS

XX Grade; Hand-Selected For Uniformity To Within .0001″ Every barrel is precision, instrument-inspected for absolute straightness and, air gauged for maximum uniformity to yield the greatest accuracy possible. Land and groove tolerance from breech to muzzle can vary only .0001″. Only a barrel that meets these demanding criteria wears the XX Premium stamp. Big Book Catalog, Issue:72, Page:168