Problem with my .450 BPE double rifle. Shooting 58 to 65 gr. of H4895 behind foam backer rod and 300 grain Hawk bullets the right barrel groups nicely right to the point of aim at 50 yards. The left shoots high and right (crossing) a couple of inches regardless of the charge. Groups not as good.

The left barrel's muzzle was banged at some point prior to my owning the gun and so has a small flat spot low and left as you hold the gun, right at the muzzle. In other words directly opposite the displacement of the bullets on the target.

Measuring a cerrosafe casting and the bore as carefully as possible I believe the constriction is .003 or .004 inches.

Assuming you agree that this may be causing the crossing shots, could I possibly correct things by counter boring the muzzle maybe .060 or .070 to take out the tight spot without making the regulation worse? Suggestions on how to go about this would be welcome as well.

I should say also that the bores are counter bored around .025 deep already; diameter of the counter bores is about .510. I don't know if that treatment was original to the gun or not.

The rifle was made by James Mac Naughton in 1898 and has steel barrels.

Many thanks.