Back up a couple of steps here. You haven't given complete information yet. For example at what distance did you test this, and how far apart are the points of impact for the barrels. I suggest you fire this gun from a supported standing position, several shots from each barrel, and use an aiming point on the target. Sort of like bench resting a rifle. Use an experienced shooter other than your brother. Find out if the problem is the gun or shooter, find out if the spread between the two barrels is shooter induced or a gun problem. Then you can start working on the gun issues if needed. If the barrels need regulated do that before you start bending the wood. Then if needed you can bend the wood.
