That was NOT caused by a bore sighter!

::)

I've seen that caused by the pilot when the crown was cut before, but the one I saw caused by that was closer to the muzzle itself. I don't think a pilot would have gone 1.5" down the bore. And it looks more like a pressure ring than a machine cut ring.

What is the history of this barrel? Factory new, have you had it since new, is this a used barrel/rifle that you recently received? What cartridge is this chambered for? It looks like the barrel was "rung", usually caused by a bore obstruction, then someone firing a bullet down the obstructed bore. It also looks like there's pitting in the bore. The obstruction could have been from dirt, snow, mud, or even a stuck bullet (I doubt that one). Usually a totally obstructed barrel will burst when another full pressure round is fired behind it. Maybe some snow or mud partially blocked the bore, causing a pressure build up and ring in the barrel.