Pictured below is an AR-15 Target rifle that I finished the build on in January. The scope is a Leupold Mark 4 LRT 4.5-14x40mm with a mil-dot reticle. LOVE the glass. The optics are clear and bright and the turrets are very repeatable. I can dial in windage and elevation corrections with absolute confidence that the scope will return to zero when I dial it back to zero.
The scope isn't really "calibrated" for any caliber. 1 click on the turret is 1/4" at 100 yards, 1/2" at 200, 1" at 400, etc. Calculate the exterior ballistics for the load you are using, range your target, and either dial in the correction with the turrets or hold over using your mil-dots (1 mil = 3.6" at 100 yards, 7.2" at 200 yards, 14.4" at 400 yards, etc.). So for example, I know my 69 grain SMK .223 load will drop about 35.2" at 400 yards. I can either hold ~2.5 mils over (14.4 + 14.4 + 7.2 = 36) or dial in 35 clicks of adjustment on the turret.
Build a range card for your rifle/load combination and you don't have to "do the math" in the field.
Hope this helps.