Re: Lowest usable magnification?
The external part of the scope doesn't move, but the internal tube inside the scope moves up and down as you adjust the elevation. One of the internal tube's limits on how far down it can point is when it is pointing at the barrel. Usually it hits the stops on the how far down the tube can move first. But if it points at the barrel before it hits the stops, then the barrel interferes with the sight picture in the scope.
As the scope is pointed further down due to elevation adjustment, you have to lift the scope (and rifle) up so the target is centered on the crosshairs. This raises the barrel of the rifle so it is aimed at an angle above the target. All this to compensate for the bullet drop over distance, so the bullet hits the target.
