That's kinda like asking "how long is a piece of string"? A great deal depends on the intensity of the loads you're shooting and the pace at which you shoot those loads.
Heat is your big enemy. If you shoot a magnum three times in rapid succession, the barrel will be too hot to touch and you can believe that throat erosion has started. But if you wait a bit between shots, the damage to your bore is much less. And, its life expectancy is much greater.
I have never had a barrel just suddenly go south. But rather, its a creeping loss of accuracy. I used a 22-250VS for several years. Years that included P dog trips to Wyoming and factory bench matches so the rifle was being shot a lot and often. Each spring, I would re-set my COL to match the eroded throat and add enough powder to bring the velocity back to what it had been. When I finally had it rebarrelled, I was seating the bullets into less than half the neck of the cartridge. It was still shooting sub-moa but an occassional flyer would pull a group to over an inch. I always waited at least 1 minute -by a watch- between shots and while Pdog shooting, I would switch off to another rifle after 10 shots.
