NDZ Performance Muzzle Wear (MW or ME) Bore Erosion Gauge Tool for M1 Garand, M1 Carbines and 1903 Rifles or most .30 Caliber bores - Stainless Steel. Our lasering process does not influence the diameter unlike other tools which can reduce your reading up to .001" showing a better bore than it actually might be. An original barrel showing .300" or .301 reading will bring much more value to a collector thus increasing the firearm collectability. Generally speaking, the muzzle will wear far greater than the throat.