Hello
Scott;
A few thoughts come to mind:
1) The issue could come from the barrel being misaligned with the action...
There are a number of reports of CZ 550 shooting out of scope adjustment range. While some of these reports come from sources that may not be entirely reliable, others come from folks, like you, who know exactly what they are doing. Additionally, since you already had two different scopes sighted on this rifle, a Leupold VXR 2-7x33 and a Leupold VXIII 1.5-5x20, and now you have a third one, you likely know what you are doing, and I accept the premise that the Leica red dot is not be perfectly aligned with the barrel.
Note that I said "the Leica Red dot is not perfectly aligned with the barrel," not "the action is not perfectly aligned with the barrel."
In truth, it is a very rare production rifle indeed whose barrel and action are perfectly aligned. This is one of the reasons why many gunsmith like to "true" the barrel and the action threads, and the face of the action.
In further truth, it is likely that there are out there many more rifles than we realize, from many makers, whose barrel and action are not entirely aligned, but because many wear modern scopes that offer a large adjustment range, the scopes do not run out of adjustment.
Based on your own experience, I observe that the Leupold VXR 2-7x33 you installed at one time only has 75 MOA of maximum adjustment. This is less than a lot of other scopes. For example, the Zeiss V4 series have 90 MOA, the Leica Magnus and the Leupold VXIII 1.5-5x20 have 110 MOA, etc. Therefore, the fact that you could sight the VXR 2-7x33 with a comparatively reduced adjustment range tells me that if your barrel is misaligned with your action - which it likely is because all productions rifle's are, more or less - then it is not dramatically so.
In summary, as far as the RIFLE diagnostic goes, your CZ barrel is likely NOT uncommonly misaligned with the action. Maybe a bit, like with any production rifle from any manufacturer, but likely not drastically so, otherwise, you could not have sighted the Leupold.
2) The issue could come from an optic with limited adjustment...
The Leica Tempus is specified to have an adjustment range of 100 MOA and clicks of 1.1 MOA each. It should therefore have an adjustment range of 90 clicks.
The Leica Tempus also has a locking mechanism that locks the adjustment in place. I do not know for sure, but it is possible that one may need to unscrew the locking screw several turns in order to allow the FULL range of adjustment.
After loosening completely the adjustment locking screw, turn the adjustment screw down until you reach the bottom of the adjustment range while counting the clicks. If you were maxed out trying to bring your shots up, you should count 90 clicks down.
--- If you count less than 90 clicks down, it is possible that the locking screw was not loose enough to allow you to go up to the full range.
Note: you are not far off, it looks like you are only short 3 clicks (3.3 MOA) to bring your group up 1.75" @ 50 yards = 3.5" @ 100 yards = 3.5 MOA
--- If you count 90 clicks, you were at the maximum of the range...
3) If both rifle and red dot are fine, the mount is likely the guilty party...
Because you were able to sight a Leupold that has 75 MOA of maximum adjustment, you should be able to sight a Leica Tempus red dot that has 100 MOA of maximum adjustment.
If you were using the full range of adjustment on the Leica red dot without its locking mechanism obstructing your adjustment (Item 2), then two possibilities exist:
--- The rifle action itself is bent, or machined defectively, and the rear and front bridges are not in the same plane. This is extremely unlikely, and I only mention it to be thorough. You can eliminate this hypothesis easily by putting a flat piece of steel across both bridges (a simple steel ruler standing on edge works fine). It should rest evenly on both bridges' flat tops and show no gap at the rear of the rear bridge flat top, or at the front of the front bridge flat top. Just check to be sure, but, as stated, it is unlikely that there is an issue there...
--- If the rifle's action is fine, the issue then is with
1 - the Rusan mount itself; or
2 - the way the Rusan mount engages the bridge dovetail; or
3 - the way the red dot is attached to the mount.
Because the two mounting holes in the Leica (same footprint as the Docter) are almost central, the Leica could be tilting nose up as a result of:
--- the surface of the Rusan mount being uneven (?)
--- the Leica bottom surface being uneven due to faulty assembly of the bottom plate (?)
--- the Leica body itself flexing due to too much torque on the mounting screws (?)
--- etc.
Solutions...
For this type of mechanical issues, I tend to believe in the Occam's razor approach: the simpler explanations are more likely to be correct. In this case anything is possible but what bugs me is that we know something critical: the rifle was sighted with an optic that only has 75 MOA of adjustment. It should, therefore, be easily sighted with an optic that has 100 MOA...
First, before anything else I would verify that the full 100 MOA of maximum adjustment were used on the Leica.
Second, the Rusan mount could be defective (bad casting or machining - it happens...) but this is relatively uncommon, and I would look at how its fits in the CZ dovetail and how the Leica fits on it.
A temporary solution could be to stick a small piece of adhesive aluminum foil HVAC tape under the rear of the Leica to tilt it downward on the base and see if this resolves the issue.
A more permanent solution could be to use a Trijicon RMR. These have 150 MOA of maximum adjustment (note: RMR is a registered trademark of Trijicon, not a generic term, the generic term is "red dot"). Since it seems you are only missing 3 to 4 MOA of adjustment, 50 more MOA (25 up and 25 down) should do the trick.
Sorry for a long post, but I am just trying to help
