When I bought the rifle i noted that the rear sight on the barrel had the notch located way off to the right up against the ear of the buck horn. I removed the rear sight, measured and drilled and tapped a hole in the center of the tang for the peep sight I installed. Test firing at my range showed the gun shooting 6+" to the left. This off of a sand bag rest at 30 yards. I know I am not the source of the error as I achieved a 3/4" group of 5 shots 6+'left of the bull. I proceeded to drift the front sight in the dovetail such that the blade lines up with the left edge of the top flat. That brought my groups to about 1.5" to the left of the bull. I can't move the front sight any further as it would come out of the dovetail, and the peep sight can only be adjusted for elevation. Thus my dilemma. Based on some of the suggestions in this thread I checked the side of the barrel with a straight edge, and there are no gaps to be seen. I dropped a bore light down the bore and the light appears to be circular, and not oval shaped. There may be a crown issue and I am going to check that next.
I'm assuming you understand how to read light rings.
One barrel kicked my butt until I found the hook started 2.5" from the muzzle and I had to put my reading glasses on to notice it. It was quite difficult to straighten without collapsing the tube, but I got it.
An inexpensive import machinist's square is a good tool for checking crowns. However, 6" at 30 yards is a lot even for an out of square crown. That much windage due to a sloped muzzle should be clearly noticeable when placing a patched ball.
I'd bush the light with tape so it is a slip fit and points straight, and check those light rings again.
Someone who has 150 barrels a year through their shop and has never seen a bent one or an arced bore isn't looking very hard.