Windage Turrets Affect Vertical MOA??

[cohunter14]

I will start by apologizing for the long post, I just want to give all the details...

I am working on my father's rifle and trying to get a load and drop chart put together for our big game hunts this fall. I took his 7 RUM out with a Leupold VX-II scope and tried to do some testing, but found out that I ran out of elevation pretty quick, although there were still clicks remaining. Because I didn't think it was tracking correct, I went ahead and brought it back to 100 yards and tried doing some vertical testing. After shooting at zero, I went up 60 clicks (15 MOA) and shot. I also did this with 100 clicks (25 MOA). What I found from that was two holes within a 1/2" of each other, 13 MOA up from my first zeroed shot. So it seemed like the scope obviously stopped tracking at 13 MOA.

I called Leupold on this and they told me to make sure that I wasn't out of MOA just from sighting it in (using all of my vertical MOA just to get to zero). The person I spoke with said that even though there are clicks available, it might still run out of MOA before that. They also mentioned that if the windage turrets have a great disparity between them, it can affect how much vertical MOA you have (reducing the original amount available).

After testing the scope, I found that I had 147 clicks down (36.75 MOA) and 111 clicks up (27.75 MOA) from zero. I also found out that I had 182 clicks available to the right (45.5 MOA) and only 73 clicks to the left (18.25 MOA).

To sum it all up, my question is this: can the disparity in the horizontal MOA affect the vertical MOA that much? This scope should have 55 vertical MOA available. Even if it tracked perfectly from the lowest setting (down 36.75 MOA from zero), if I add the 13 MOA that I got when shooting, it only gets me to 49.75 MOA.

Sorry for such a long post, but I want to make sure I have this all straightened out before trying to send the scope back to Leupold for repairs. Worst case I know I can add a 20 MOA rail, but I figured I would ask you guys first. Thanks!

 

[Dr. Vette]

What bases and rings do you have currently?

Think of scope adjustment as working inside of a circle with MOA sized squares inside of it, sort of like this:

The more you adjust the vertical (or horizontal) the less of the other you have available. At the center you have the most adjustment, but as you get closer to the edges of the circle your available MOA decreases. In the picture above imagine adjusting your horizontal out to the 8 mark. Note that you now have only +/-4 available for vertical adjustment, not +/-9 as in the middle of the circle.

I suspect you're running out to the edge of the "circle" in adjustment vertically because you've used up a fair amount horizontally.

I hope that makes sense.

Now, the type of bases and/or ring you use may "use up" some of your horizontal adjustment by being misaligned to your barrel. This is why I try and line my scopes up to keep the horizontal adjustment as close to the midline as possible before I ever fire the first shot.

 

[cohunter14]

That makes perfect sense, I completely understand now. I don't have the rifle with me, but I am guessing that it is just Leupold bases and rings. How can you go about changing the bases and/or rings to get the scope to line up better? It seems to me that there isn't a ton of adjustment available once you put the screws in the base and attach the rings, but maybe I am missing something...

 

[Dr. Vette]

Those big screws for the rear ring? Those are called Windage Screws for a reason. My guess is that adjusting the windage screws (and then properly torquing them to 45 in-lb) can get you back where you need to be.

You might still need to change rings (Burris Signature come to mind) to add MOA to your vertical adjustments, but start with the basics. If your scope is out of line with the barrel now is the time to line it up.

 

[cohunter14]

Okay, I get my stupid points for the day

Thanks Doc

 

[Dr. Vette]

No problem. You are by far not the first to have this issue, and guaranteed not to be the last.

Let us know how it works once you get it adjusted.

 

[cohunter14]

Will do, thanks!