I have a FN PBR (similar to a Winchester Model 70) in .308 Win and am looking at installing a one-piece scope base that has a built in 20 MOA of elevation. I am wondering if there are any drawbacks to using such a base. Of course, I realize that the built in elevation will require me to dial back a fair bit on the elevation knob of the scope to get a 100 or 200 yard zero. To be specific, however: -Is there any adverse effect on the scope from using it with elevation adjusted way down to one end of its adjustment range? Will this cause any optical distortion, added parallax, or any other problem in scope use? -Will this limit my scope options? Some scopes only have 50-55 MOA of total internal adjustment. Are they normally designed with the 0 MOA point being right in the middle of that range (therefore allowing 25-27 MOA of downward adjustment and accommodating the 20 MOA base elevation), or do they typically have greater upward adjustment than downward adjustment? -Any other drawbacks I should be aware of? I already have the 20 MOA base, which I got for free. I could instead buy a 0 MOA base for $40 or so but would rather not unless the 20 MOA base is going to cause me problems. I'm aware that the 20 MOA base shines at long range in allowing you to use almost the full elevation range of the scope to dial in elevation for long shots, however while I would like to try long range shooting the longest range I have available is only 300 yards, and the longest that's convenient is only 200 yards, so I won't get the benefits all that often.