Just got back from the range with my new rig. It's a 300 Winmag set up as a light weight walking rig with long range capabilities. Optics are a Leupold 3.5-10 VXIII w/turrets in Talley LW's. Problem is this: sighted in for a 200 yard zero, I've only got 4/5's of a complete turn in elevation left...so I know I've got to shim the rear base. I've never done it before, though have some inkling how to do it. Questions are this: 1) I've got two complete turns of down left in the turret. Approx what thickness do I need to shim the rear base to recover those turns? 2) Is it necessary to lap the rings after shimming? Wondering if the resultant offset will induce unkind stresses into the scope tube? Thanks in advance for help from those that have BT/DT.