I once shot a friend's rifle which had the muzzle polished lopsided. I think the top was worn, and this threw the ball upward and it grouped well. I no longer remember how I figured this out, but the suggestion to file the muzzle will work, but you don't have to file the whole muzzle face, just the crown, and not much, either I once had a reject-Green River barrel, .40 caliber maybe 15/16" about 36 or 42" long, can't remember, and it had about three bends in it. The suggestion to bend it in the crotch of a tree did not work. Nor bending it with C-clamps. A gunsmith friend put it in his barrel bending vise with some kind of hydraulic jack, and you would not believe how much that barrel had to be bent to effect a straightening. In three places, as I remember. Like maybe three inches up at each end!
A simpler method would be to make a tang mounted peep sight. Take a piece of metal lumber strapping, or a hacksaw blade, drill a hole for the tang bolt, bend the back end up at right angles and the tang bolt holds it in place. You can swing it to the side for windage correction. You can mathematically calculate how high the hole has to be, or find the elevation (and windage correction) by shooting trial and error. You could just duct-tape it on the tang with multiple vertical holes until you get the right elevation. You can also try different sized holes till you find what works, maybe 1/8" up to 1/4 inch size. Center your front sight and leave it uncut. Or you can look at Track of the Wolf's web sight and probably find a rear sight that can be filed to work. I have made several rear sights for Hawken rifles, hacksawed and filed out of a piece of 1/2" angle iron.
