FOXFIRE, this is common with older double rifles that have been used quite a lot. It is usually the result of wear in the right barrel. The right barrel being the first barrel fired, gets more use than the left barrel. Many of the shots taken on game with the right barrel are all that is needed, so the left barrel is not fired.

The example of 1" to 1.5 " apart is not enough to worry about if this is at 50 yds or farther, as long as you are aware of the placement of each barrel. At close range, like under ten yds you will probably not notice the difference between the barrels. Under ten yds, is where they must absolutely hit the same place! 1" to 1.5" @ 50 yds is tighter than most people can hold, under hunting conditions, and if it is a 100 yds, it is not a problem that needs fixing! The only real fix for the verticle spread caused by wear, is rebarreling, and 1.5" is not a problem, I'd worry about.

I would predict the right barrel shoots the highest, because of less resistance from the bore, causeing it to not develope enough pressure, hense less speed. One thing you can do with this rifle, if it bothers you when hunting dangerous game is to reverce the shot sequince, because I would bet the left barrel is shooting closer to the sights. By reversing the shot sequince and shooting the left barrel first, the first shot will likely be spot on, and if a charge insues, the closer the Buffalo/ele gets, the closer the right barrel will be to the sights. The left barrel will give more velocity, as well, at longer range, and off the end of the rifle, the right barrel will be closer to the sights. I'd find out, however, on paper before hunting a mad lion, if I were you!