what rifle is it.?
what scope is it,?
if its a 40-44 mm objective get medium .. my mtc mamba lite 44mm is perfect in medium mounts, but if you had a front parallax scope you might need high.
if its 50 mm get high
I would get some sportsmatch uk, 2 piece, double screw. there about 17-20 quid but well worth the extra few quid, they have never let me down and I have them on all 3 of my scoped rifles.
better to position correctly than a 1 piece aswell, and just as effective, even on a high recoiling springer, if you fit the arrestor pin