In the course of locating the disassembly instructions, I found the original sight-in target for the rifle and it shows precisely the same shot distribution as I experienced. After removing the fore end, I was able to examine the barrel adjusting mechanism, and I think I understand how it works. Removing the fore end was a monumental task in itself, however, involving a long thin screwdriver and a very long thin screw. The fore end cannot be removed with the barrels mounted on the receiver, unlike any other O/U I have ever experienced.

My camera is taking photos with no problem, but for some reason when I transfer them to the computer they end up being displayed as 16 tiny images instead of one large one. I have pored through the instruction manual and can find no solution for the problem, so I guess I'll have to call customer service. Ugh.