I had this problem on one of my rifles and I was able to loosen the block screws front and back and shift the front block opposite to the windage I needed and the rear block into the direction I needed to get zero windage. There is enough slop in some of the base blocks that you can get enough for center. 
With the blocks set at 7.2" it don't take much to move center adjustments.
I also have made adjustments by placing a shim in the dovetail on the rear mount but this would need the posa type rear mount.

I'll try Arnie's solution but I believe this a orphan mount for some other purpose. The windage adjustment is defintely .180 short of being where it needs to be. I think my solution to stick the mount in my parts box and use another is the answer. Some day. I;ll find the answer.
Thanks all.

Not questioning the problem, but can’t see anything wrong with it from the photo. If we had photos equal to the ones Nuclear Cricket posted something may show up. However internet diagnostics are questionable at best.

I would still run a detailed and recorded test, extreme range in reading windage & elevation barrel = range of micrometer travel. Then measured extreme movement scopes tube knobs plunger backed off= range of possible tube movement. Compared to other Unertl measured range It will quickly tell you if the mount  is altered or defective in some way. Separately testing micrometer and tube movement will narrow possible problems. Elevation
and windage movement range should be the same too,another possible clue 

Boats

JLouis wrote on May 16^th, 2022 at 9:51am:


Amen to that.  I have a rifle barrel with those problems.  Very difficult to zero.  Too bad, as it is one of my go-to range rifles.

Chris,

That pin is to make sure the screw does not turn.  It makes it very difficult to replace a broken screw!

Jack

Try another photo. If you compare this pic to the one posted by nuclear cricket, you will note that the zero on my base sits considerably furthur out. The side of NCs mount is straight where mine has a raised boss between the verical rail of the sight and the zero liine. Amounts to about .180 which is how far to the right of center the scope sits when the mount is set at zero.
  The bases are correct, verified with another scope. The adjustments function correctly, just that the scope cannot move far enough left to get a zero

Here is my Unertl mount on a tube sight.  It is hard to tell from your photo, but the clearances inside seem much less on yours.  Almost like it is a 7/8" tube.  Got me puzzled.

Jack

Jack, you get the "Bingo" re the 7/8" tube scope tube in a 
"standard" Unertl mount. 
I will say  though that Saratoga Bill's mount has taller
Bosses, than your Varmint model. Especially on the windage 
beltfed/arnie