Rainbow, if the muzzle's bore diameter is a bit under 7.63mm, that's a bit under 0.30034". Many fine match grade 30 caliber barrels are right at .300000" which that one may well be at. It's the groove diameter that matters most. Push a .310" (7.874mm) diameter round ball from breech to muzzle, then use a good micrometer to measure it's diameter. That's the groove diameter. Good 30 caliber match barrels have groove diameters about .0005" (0.0127mm) smaller than bullet diameters used in them.
Barrel wear is best measured at the origin of the rifling at the back end of the barrel. Very little wear happens at the muzzle. If that barrel's got more than 4000 rounds through it, it's accuracy has degraded about 40%.
I've seen some very ugly match barrels win matches and set records; they're just a tool to shoot bullets into paper, not something to win beauty contests with.
Extra velocity with a longer barrel gains very little in useful range for hunting purposes, but it helps as bullets drift less in cross winds and keeps some bullets supersonic all the way out to far distant targets.
A 25 inch barrel will shoot the same bullet out about 100 to 125 feet per second faster than a 20 inch one will. That's the only difference ballistically. The longer barrel is easier to hold on target as it's heavier and swings around less when you're aiming it.
And "match" barrels are usually those with very uniform bore, groove and twist dimensions. Bore and groove diameters held to 0.000254mm (.0001") tolerances and less than 1% change in twist rate from breech to muzzle. They can be any length or diameter. And they're very well stress relieved, too.
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master
Last edited by Bart B.; March 14, 2013 at 04:49 PM.