I'm mounting a 4-16 x 42 nikon monarch on a TC prohunter. I want to use leupold dual dove tail rings. Should i use the medium or high.

Contour barrel........ low rings, depending on the bases. ??

I did a writeup a while back on measuring scope ring height specifically for this question. Take a look, it will help you understand how to do it exactly.

My instinct is to go with medium, but you'll want to measure to be sure.

Agree on the medium rings.

I just put a 3.5-10x42 on a mountain rifle with Leupold std dovetail rings, I used low on mine. Can't say for sure if it will work on yours. I would think med would work for sure, and the low's may.