I once spoke to a Leupold tech via telephone and he confided to me that fully 2/3's of the scopes that are returned to Leupold for "repair" really aren't broken at all. I asked if Leupold informed the scope's owners that their scopes weren't broken, and he said "rarely." It would seem that if folks go to all of the trouble of sending in a scope which they believe is broken, they want something
done. Telling customers that there is nothing wrong with their scopes gives them a "1-2" punch, so to speak; they don't get anything done to their scope, and they are also made to look inept for having sent in a fully functional scope for repair. So Leupold generally just gives the scope a good going over, charts the erector movement, and returns the scope.
But what would cause someone to think that a scope had "failed" when in truth it really hadn't?
The most common reason for scope sighting problems which isn't related to the scope itself would be, of course, a mounting problem
If you mount a scope on a base which isn't aligned closely to the barrel's bore (that's bore
, not necessarily barrel, since some bores aren't drilled straight through the barrel) you may have a hard time zeroing the scope at particular ranges.
If the base is slanted up or down, as opposed to being parallel with the bore, you'll need to dial in quite a bit of elevation correction to get on target. Normally, this won't be much of a problem unless you run out of "come ups" for that 600 yard target you're trying to hit.
Or, if the scope base is off to the left/right with relation to the bore, you'll need to dial in quite a bit of windage to get zeroed. Here's what can then happen:
(Sorry about the blurry images... just imagine this particular "scope" is a BSA). [img]/ubbthreads/images/graemlins/laugh.gif[/img]
Look at the top image. The green circle represents the erector inside the scope tube. In the top image, the erector is relatively centered, with plenty of room to move up/down/right/left. This is how you hope your erector will align when you zero your rifle.
In the second image down, the erector has been dialed over to one side. This may be to compensate for a base/ring system that isn't in line with the rifle's bore. While you can zero the scope for closer ranges, you won't be able to dial the elevation up to reach longer ranges because, as you can see in the diagram, the erector will hit the inside of the scope tube at about 2 o'clock (or 4 o'clock if it is moving down). This scenario is what is often the case when the scope will zero just fine at 100 to 200 yards, but the shooter runs into trouble when he tries to get a 300 yard or farther zero. A scope which fails a BOX TEST
may merely be a victim of a bad mount, and in fact have no internal problems at all. Further, if you find that your windage zero drifts off to the left or right as you dial in elevation, you may be forcing the erector to follow the curve of the inside of the tube (slightly), thereby forcing it aside.
In the third image in the stack, you will see an example of a "dialed up" erector; it's at its upward limit of movement. If you were to try to dial in 15 MOA of windage at this high elevation setting you might get half of that. Then the erector would hit the inside of the scope tube and stop. The shooter might say "Damn. This scope works great except when I try to dial windage at 1000 yards. I'm gonna send it back to Burris." (or Leupold or USO or whomever).
The larger scope tubes don't really have any advantage at all as far as light transmission--but they have a significant advantage when it comes to internal adjustment room. A 30mm scope tube could be mounted on a "crooked" base and ring set and still dial right in, and likely work fine as far as "come ups" too. Therefore, one might replace a 1" tube scope with a 30mm scope and find that a tracking problem has gone away. The 1" scope will be blamed, but a faulty mount may be the true culprit.
The point of this whole piece is to get folks to understand that in many (perhaps most) cases where a well made scope won't dial the correct elevation it really isn't a scope issue at all; it may in fact be a mounting issue.