I have no set time parameters for when I change barrels. When I get tired of shooting one, I change to another. I make it a point to take the rifle down to the bones when I do & service / check everything out.

Even though I have never found anything of critical nature that needed attention, I want to see how it wears and / or holds up over time.

I can think of one time where I didn't have to zero in the scope & I attributed it to pure luck.