In the rimfire spectrum of accurate rifles, folks on the US Olympic Team used to rebarrel at around 50,000 rounds. But that was before the mid 1980's when the priming compounds changed and more frit was used in the mixture. Thereafter and today, their barrels last about 30,000 rounds of best accuracy. This applied to the 1/6 MOA at 50 meters and 1/3 MOA at 100 yards the best ammo/barrel combination would get back then. Nowadays, they pray they can get 1/4 MOA at 50 meters and 3/4 MOA at 100 yards.