If porting the barrel doesn't affect accuracy, which is just a hole all the way through, then I don't see how a small ding or gouge can, either.
I had a deep pit in the bore of my M14-3, which was there when I bought the gun. I was concerned until I figured out that if the bore was ported at that spot, it would shoot fine. It was about 1 inch from the muzzle. The pit was about 1 mm across and half that deep. The gun grouped nicely, as well as I could tell from a rest.

Best,
Rick