I think calling it shot out might be misleading. Most barrel ware is due to abrasion from the ramrod. That is not to say a barrel can't be shot out, but in this day and age when the majority of the shooters, shoot much less, than in the old days, its highly unlikely. A good test to see if it is barrel ware, or is truly shot out, is to cut a couple of inches off the muzzle, and recrown it, and see if the accuracy returns. The barrel material used today is much more ware resistant than the wrought iron of old, making barrel life much longer.
Another facet of this puzzle, is what is your standards of accuracy? Are we talking about match grade accuracy? Hunting grade accuracy? Plinking grade accuracy? It all come down to degree of acceptability. What is acceptable accuracy for one, is not for another.
Hungry Horse