Re: question about useable turret travel
There are a couple of issues concerning internal usable travel.
1st there's the issue with windage. If the erector tube ( that thing in the middle that moves when you adjust the scope) is in the center as far as windage is concerned, then the elevation adjustment can be used to its full extent top to bottom.
If you have some windage dialed in, as from sighting in your rifle, the erector tube may not be in the center of the outer tube, and as you get near the top or bottom of the adjustment, the erector may contact the outer tube. When this happens, the adjustment may still turn but the erector is mechanically captured and no adjustment takes place.
The next thing is a weak erector tube spring, or an overly long or thick spring.
A weak spring shows as inconsistant elevation adjustment as you near the upper limit of travel, or as a wandering point of impact on an otherwise stable rifle/bullet combination.
An overly thick spring shows as an inability to get to a 100 yard zero; you're point of impact may be several inches too high at 100 yards for example.
Hope this long winded expanation made some sense.
Mike ,Granbury, Tx