If you're referring to BDC or caliber specific turrets, you're correct. You cannot just slap one on and go. It may put you in the ballpark if your caliber is running in their range of velocities, but don't count on it. Exposed target turrets will help you in long range shooting, but only after you do load work and build dope charts. On my AR, I have a 100yd zero with my 50gr. V-max, I have range results that say that my 300yd zero is 24 of my 1/8" clicks up. This was data collected in the field by backing up to 300yds and shooting to verify it. I document the number of clicks it took to get back to bullseye. Once I have my ranges I run them through a ballistics program like JBM and change velocity and Ballistic Coefficients until it matches my chart at the 100yd marks. That'll give me the in between ranges. This is all subject to change based on changes in velocity, range, altitude, shot angle, wind deflection, and scope height to name a few variables.
