A worn out barrel shows up first at longer ranges.
There is truth in this statement. As we put more rounds on a barrel, we usually see a drop in X counts at 600 yards as the first sign it is nearing it's end. Scores will drop next and flyers will appear at the short lines (200 and 300 yards) more frequently. It's not uncommon that while this is going on, the barrel will continue to pump X's on a 100 yard reduced target. The more frugal amongst us will turn that barrel/upper into a "reduced course only" upper. The no-nonsense folk pull the barrel at the first hint of a drop in performance and add a tomato stake to the garden.
My learning is to always check your accuracy at the maximum distance your shots matter at.
