Are you boresighting after each shot? If so the adjustment is opposite. The "u" actually makes the crosshairs go down(in relation to the rifle) and the "d" actually makes them go up. Try turning them in the oppoiste direction a few clicks and see what happens. The only other thing I can think of is that you have the wrong bases and rings for your rifle, or the scope is broken. But if you were boresighting after each shot, that is definately the problem.

this often happens, but I must say at 13" you ahve a bad case of it! If the rings are swapable, such as Talleys, put the fron ring on the rear base and rear ring on the front base. If you are using something like the Redfield system, this is not possible.

Burris SIgnature rings with the swapable ring inserts will fix this problem.

Or you can shim the bases (I don't like this method, but it works).

Or you can have some one machine the base to get it at th eheight you need.

Or you can try swappinmg rings and bases. TH emanufacturing toleracnes with rings, bases, and front and rear reciver bridge hi/lo is usually bordering on atrocious. If you get two or more of these at the end of the manufacturing specs where tolerances stack against you, you get screwed like this. But man, 13" is a lot!

THis is assuming there is not a ton of upward pressure on the barrel. if so, try reducing that first.

I say go with Burris SIgnature rings and bases and be done with it. Can make almost all adjustments with the rings and then you can keep your scope internal adjustments close to center where the yneed to be