The tapered barrel simply cannot be the cause of the gun shooting low. It could only cause the gun to shoot high. That's why thelong range shooters can use machined bases, to get the extra range.

Look at it this way. Imagine your gun is hitting dead on. Then put a big shim under the rear scope mount. This would cause the scopebe "looking"downward in comparison to what is was before.You'd have to raise the gun to get the crosshairs back on target, and you'd shoot high.