Muzzle gauge reads the wear on the muzzle and yes you should pay attention to that number. Here is how it reads.
Carefully, so as not to damage the barrel's rifling or the gauge, insert the the gauge into the muzzle as shown. Read the gauge directly from the side. Observe where the muzzle "falls" on the gauge.
0.0 indicates a .300 diameter bore, that is, .30 caliber, new, perfect.
0.5 is like new, .3005 caliber. Proper re-crowning will perfect the crown.
1.0 is excellent for a used barrel (.301 cal.) Re-crowning should make it like new.
1.5 is good (.3015 cal.). Proper re-crowning should make it excellent.
2.0 is fair (.302 cal.). Proper re-crowning should make it serviceable.
2.5 is poor (.3025 cal.). Proper re-crowning might make it serviceable.
3.0 or more is a "bald tire" and is now a British .303 caliber barrel. Replace barrel
