If your windage is good at 50 yards, it should be good at any range, regardless of a bent barrel or crooked bore. If you think about it, what you're suggesting is that the ball is traveling in a sideways curve, which is impossible, except in the movies.
Sounds to me like a classic example of canting the rifle. If you hold your rifle cocked a little sideways when you shoot, it will throw that ball more and more to one side as your range increases. You can zero the windage at a certain range, but it will hit to one side when range changes.
Lots of ways to check for canting. If you shoot from a bench, steady the gun in place and step back behind it to see how it lines up with gravity. If you shoot offhand, just cant the rifle past where it feels comfortable to you, in the opposite direction of the windage drift, to see if the ball strikes more along the correct windage path. Or, ask a friend to observe how the rifle looks just before you shoot. You're looking to have a verticle line, in relation to gravity, from the sights to the bore, that's what all ballistics are base on. Hope this makes sense and helps. Bill