I'm having problems with a Bock-Drilling, that has 2 rifle and one shotgun barrel. The .22 Hornet barrel should regulate to approximately the same POI at 100 meters as the 7x65R rifle barrel. However it shot well to the left and up, almost off the target. I took a large bag of wood-wool, (like straw but made of wood shavings. I use if for lining wild-duck nest boxes), and shot the rifle holding the forend while leaning on this bag. The POI was the same as the benchrest, so this wasn't really the issue.

I then took a jewelers loupe (a magnifier), and looked very carefully at the 2 muzzle crowns and found they were chewed out one side - the opposite side to the direction the bullets were biased to. I had these crown chamfers recut but the damage was still visible and the POI still unreulated. I then had the muzzle crowns set back perhaps 5mm until the crowns were completely clear of any damage. Any deeper and the danger was that the soldered muzzles would be comrpomised. The appearance is still quite acceptable. This work resulted in 1" (MOA) 3-shot groups for the 7x65R and a much better regulation for both barrels. It's not perfect yet, but it's a lot better and I'm now looking for the right powder/velocity/bullet load that brings the 2 together.

So have a very careful look at your muzzle crowns. If the bullet goes up, look especially at the lower crown for that barrel. What happens is that as the bullet is clearing the barrel, the damage allows the powder gases to blast by while the rest of the bullet is sealed to the barrel. This tips the bullet slighly in the opposite direction.

Also, it's no bad thing to find out what the factory regulated the rifle with, and use the same load or as nearly so as you can make it. For instance, this Ferlach made rifle was made in an era when .22 Hornets were uniformly 45 grain and 2,400 fps. So that's a pretty good place to start, though increased velocity can, of course, shift the POI and, if you're lucky, shrink the distance between the two barrels POI.

It can be an option to load different loads for the left and right barrels, that regulate closer. However, if you then mix them up... !!! If you went this route, which I don't really suggest, you might look at using nickel-plated cases for one of the barrels, so they don't get mixed up. I use nickel cases for solids so they don't get mixed up with softs.