Is it brand new ? If so I would return it immediately. When you rotate the zoom ring you are moving an optical group forward and backwards and that group is not moving coaxially to the scope centerline.
Having said that, how the heck did you run out of adjustment zeroing the scope at 25 yards ? Something is way off with the rings/bases. It should not take much more than a few minutes on the elevation and windage to dial a scope in.
Re-zero the turrets to the center of their movement and bore sight the rifle then figure out what is going on with the rings. Shooting low means you are aiming high. Is it possible the front and rear base are reversed ? Of that the front and back ring are different ? Sure those are the right bases for your gun ?
Mmm according to this http://www.castbullet.com/misc/m60.htm
it does not look like bore sighting is possible. Is there an integral 11mm dovetail in the top of the receiver ? The rings bolt right to that ? If that is the case and they are the right rings, it suggests that the barrel/receiver are crooked and the scope is pointing up in the air.