When I set the rifle up at home, I used a "Nikko Stirling Scope Alignment Device". The kind that you choose the rod size to poke into the barrel and align the cross hair against a grid in an optics tube.
The rod has a small spring wire at 12:00 thats suppossed to be light enough to just stop the rod from sliding out.
I've had great load testing groups with this barrel and in 3 fullbore shoots, I've dropped 3 points so I hadn't questioned it. After the last shoot I noticed that the star on the crown was missing a leg at 12:00. I borescoped the muzzle tonight and found a 2" long HEAVY gouge at 12:00 running straight up the barrel despite the lands and grooves. It looks aweful.
I can't believe it was shooting so well.
I pulled out that Nikko Stirling P.O.S and set it up to find that the spring wire on the shaft married up exactly with where the gouge stops.
I've used this device to setup a few rifles before and never seen this. It may be a tight bore??? I know for certain that I didn't use the incorrect rod.