Well done getting there in the end. For what its worth this may help to explain those misses.
The original scope, fixed power (with a mildot or bdc reticle? )gave holdover values that worked.
You upgraded to a variable power, Im guessing with the same reticle and zeroed it correctly so in theory the hold overs should work.
The diamondbacks are second focal plane scopes meaning the reticle graduations are true only at the scopes maximum magnifaction, so if you wound back to 6x which you are familiar with each dropmark will be 2.25 times greater than you expect leading to exasperation and second guessing
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