For my target guns I use Burris tactical rings with 6 screws on my one piece bases. As far as height, a lot depends on what type of barrel and where your scope is placed on the rifle. I'll lay a 1/2" bolt/rod/drill bit across the front and back of the base and set the scope on them and measure the clearance between the objective housing and the barrel the subtract that less the clearance you want from 1/2" to determine ring height.