[Bart B.]

In my experience, the rougher the barrel's bore and groove surfaces are, the more rounds need be fired before the tall micro hills and mountains scrape off enough bullet jacket to fill the valleys between them so no more's removed from subsequent bullets. Too much scraping off of the jacket tends to unbalance bullets; they don't shoot too accurate.

Barrel smooth or rough amouts are typically measured in "microinches;" millionths of an inch heights of those tiny hills and mountains. Most match grade barrel makers don't want to get less than about 8 or 10 microinch finish as any smoother causes too much friction of the bullet jacket and more jacket is rubbed off. A 10 to 15 microinch finish seems about best for least amount of bullet jacket scraping as well as excellent accuracy. And they typically shoot the first bullet to the same point of aim as a dozen or more fired afterwords.

A match grade barrel maker told me of a law suit filed against Shooter's Choice shortly after Shooter's Choice bore cleaner came out. Someone used it on their favorite rifle and the rifle's accuracy suddenly went south; way south. That person filed suit against Shooter's Choice. So, Shooter's Choice, in company with the barrel maker, proved that his old barrel had not been cleaned all that well over the years and Shooter's Choice bore cleaner "cleaned" the barrel of all the built up fouling uncovering the pitted surfaces in the first few inches of the bore that was otherwise perfect as made by the barrel maker. The case got tossed out of court.

Best way to observe this is watching the leade of a .22 rimfire match barrel erode away. Erosion starts at the bottom, or 6-o'clock position. Powder and primer residue settle there. Bullets push it down the barrel and until it's embedded in the soft lead bullet then it microscopically scrapes away barrel steel. As more rounds are fired, that area at 6-o'clock starts getting darker and wider than the rest of the leade area. That dark part moves up on each side about one "hour" for every 10,000 rounds fired. There's more rough area that holds the fouling as erosion increases. After 30,000 to 40,000 rounds (depending on the match ammo used), that dark ring works is now up at about the 9 and 3 (or 10 and 2) o-clock points and accuracy has degraded from 1/4" at 50 yards to about 3/8" or from 5/8 MOA at 100 yards to 1 MOA, it's time to rebarrel. Or set the barrel back two inches; that's often as good as buying a new one.