In addition to throat erosion and copper fouling, there is also thedreaded "hard powder fouling" that can cause a drop off in accuracy. I would generally expect a .22-250 barrel to last about 2,000 rounds under less than ideal conditions, and more than 3,000 rounds under optimum conditions. If you can gain access to one of those Hawkeye bore scopes, like Big Country recommended, you can eliminate or confirm throat erosion right away.