5x bottom end on mk 12? Really? Just get a #masterace ZCO 420 if going that route.
I use 2.5-20nx8s on a couple mk12ish ar15s and 6.5 ar10
going to try a vortex 1-10 on a 15 cause I hear they work great with clip ons
I have a couple 2.5-10x42s on 15s also and they work...