Try mounting it with the C clip on the side mounting bolt removed .
These directions came from 45ACPKing ( formerley m14Doctor) he has mounted many many of these mounts .
Installing An ARMS18 Mount by M14Doctor
I find it odd that so many folks have issues getting ARMS 18 style mounts to align correctly.
Here's my tips:
* Get rid of the horse shoe washer on the inside of the retaing bolt. This lil bugger is what offsets the front of the mount... I ditch it everytime.
* The rear screw that attaches to the stripper clip guide key. This has an adjustable pad that is key to alignment.
* Remove the screw and use a slot screw driver to adjust. First step is to back it out so it doesn't make contact upon "test fit" install. Same goes for the front pad.
**on my promag version this rear adjustable pad was installed backwards from the package. The slotted face should face up, away from the receiver.
* Snug fit the side bolt and set a 3/4 or 1" dowel on the mount. Observe position.
* Then slowly bring rear pad to just touch the clip guide key.
* Install rear screw to just snug, then fully tighten side bolt
* Check alignment and level.
* These can now be adjusted by removing rear screw and lessening or increasing the tension of the rear pad. Reinstall screw and fully tighten.
* Finally adjust front pad until it just touches receiver.