You can work out how many MOA you'll need by using some simple maths.
1) Wind the elevation turret from one extreme to the other and count the MOA adjustment available i.e. if it turns 30MOA from hard stop up, to hard stop down, then ideally you'd want it at 15MOA (or whatever half of your adjustment range is?) when zeroed.
2) You're 3'' high at 25m, so that’s about 12MOA.
3) So you need 12MOA + 15MOA (or half your adjustment range whatever that is???) = 27MOA of shimming or about 6.75'' (171mm) of height on your target
Next Stage:
4) Measure the gap between the rings (say 150mm?????)
5) Use a ratio equation to work out the rough thickness of the shim required:
a=total drop required
b=distance to target
ratio = a/b
ratio = 0.171m / 25m = 0.00684
Now use this ratio, but apply it to the gap between the rings (instead of the gap to the target) and you'll know the difference in height required between the two rings i.e.:
ratio x gap between rings = shim thickness
0.00684 x 150mm = 1.026mm (thickness of shim required)
Just replace the numbers above with the values you've measured (gap between your rings and your scopes total MOA adjustment) and you can then work out the thickness of the shim required like I've shown.
kj
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