by Gwion » 28 Jun 2017, 6:19 pm
So, if i'm not completely mistaken, that should be your 19mm (make it 20mm) - 12.5mm (half diameter of scope tube will be bottom of tube: make it 12mm for the extra 1/2mm clearance) and you are left with 8mm as minimum ring height (0.314").
Any of those rings should be fine depending on your natural cheek weld. No point having it too high and looking at the bottom of the scope or too low and looking at the top of the scope. Ideally you want to be able to bring the rifle up, naturally place your cheek to the stock and be looking dead down the center of the scope.... ideally.
You could play around with the rifle and a ruler placed roughly where the ocular lens will be and see exactly where your eye looks when you "mount" the rifle. This will probably need about 18 sets of hands to do satisfactorily, though and is probably a bit OTT, but that's me. Subtract you 12.5mm from this number (center of lens=center of scope bell/tube) and choose the rings that are closest to that size.