You are not relying on the scale on the Elevation Drum now, are you? It has to have been properly indexed or the numbers on it are meaningless. That's what the big screw on the left side of the sight knob is for - reindexing the sight drum so the numbers match the yardage.

Many M1/M14icon users count "UP" clicks from the bottom, and ignore the marks on the drum. Usually 8-11 clicks up from the bottom gets you "on" at 100 yards, although guns vary a little.

A laser boresighter will give you mechanical zero, but you have to shoot it to be sure. CC