Hey Mike,
Remember that there are only so many elevation "clicks" that can be had inside your scope. The actual end - end limit varies between manufacturers, but Target scopes typically have a bigger range. Remember also that bullets in flight trace a parabolic curved flight path, with the lower powered bullets tending to arc more the farther out they go. Most scopes cannot be adjusted then for a point of aim impact at 800-1000 yards, and even if they can, they are at the far end of their adjustment, in other words, they are near to the stops.
This is where the tapered base comes in to play. They are thicker on the side nearest your eyeball, therefore pointing the scope a bit further down with relation to the bore sight then a normal scope base. This allows you, the long distance shooter, to get a zero on your weapon at 800 - 1000 yards without having the reticle crammed way down at the bottom of your view.
Keep in mind that this is a long range target shooters gizzie, and that it really doesn't have a use on a rifle that will be used at ranges under 500 yards.
Good Luck, Unkel Gilbey
[This message has been edited by Unkel Gilbey (edited January 23, 2000).]