Quoted:
In particular on a AR10 platform with a 3x18 scope (vortex razor hd 2). I'm starting to play around with the long rang stuff but also looking to to hunt with it. I am planning to buy a Geissele in 20 MOA but want to hear about the cons.
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What is the range you are shooting?
Even if you shoot 1,000 meters, based on what you have (7.62 X 51), 10 MOA base will be more than enough.
The down side of 20 MOA mount is, if you have a large objective, a 20 MOA base will lower the objective enough to touch or interfere with your forward rail, or you might need higher rings.
Yes, the +MOA bases tilts the scope down wrt rifle.
I have 20 MOA + NF ATAC on my DTI SRS, and I wind up adding a 1/2" spacer between the optics base and the rifle, because the objective touches the front rail.