Anyone who has purchased a M1 Garand from the CMP has certainly heard of the infamous "muzzle wear" measurement. It's one of the checks that the CMP armorors do as they grade the rifles for sale. For instance, they guarantee that their Service Grade M1s will gauge 3 or less at the muzzle. But what does this actually mean? Here is a bit of data to help make sense of the numbers:
- 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
As noted, re-crowning can sometimes help improve a muzzle that has gone a bit slack. It's a simple procedure that many armorers can accomplish (check out our list of Garand armorers), and it's even something the do-it-yourselfer might want to accomplish on his own with a little research and the right tools. Lots of factors can affect muzzle wear (including improper cleaning!), so you should gauge your rifle at least once a year. I bring muzzle and throat erosion gauges to the matches, so please feel free to contact me about measuring your rifle's barrel.