ARMS 18 mount issue

[Holleyman]

Anyone here run into issues with the ARMS 18 mount not mounting square on the reciever? I have a Norc and it seems the scope has a degree or two off to the right. I checked squareness of the barrel bore to the reciever, it is straight. I have it mounted now, it does seem straight but I had to push the rear of the dovetail over to the right side as far as I could, tighten the allen head screw, then tighten the main screw on the left side of the reciever. I expected the mount to basically sit straight by mounting it with the large screw first. Am I missing something here?

 

[furet]

Oh boy, I had some problems with my #18, My drift was the opposite of yours. Having said that, you need to look at different things first.

There is a post about mounts that is stikied.
First you need to look for contact points between the rail and the receiver. It may be touching on the top or front edge of your receiver.
Also it may be touching the stripper clip mount.
When installing it don't put the stripper clip mount piece in and backoff the front pad, look for any contact points, the mount should only touch the vertical & horizontal keys. Use some soft clay between the mount and receiver when installing to see if clearence exists.

Also look to see if the mounting hole is centered with the vertical key slot, mine has a slight offset, you may have an issue with the slot not allowing the screw to center itself thus causing drift.

Get back to see progress

taken from http://www.canadiangunnutz.com/forum/showthread.php?t=35091

..Side Three Point Scope Mount Fitting on Commercial M14 Receivers
There are five points of contact between the side three point scope mount and the receiver that may cause improper fit up with military design side three point scope mounts when installed on commercial M14 receivers. The surface contact between the left side of the scope mount and the left side of the receiver is of primary importance. The more contact between these two surfaces the less likely the mount is to shift from firing recoil. The scope mount should be tested first for fit without the stripper clip guide dovetail key supplied with the mount.
Receiver Bolt Hole - The USGI M14 receiver drawing specifies a distance of 1.500 " + or - 0.003 " for the distance between the bolt hole centerline and the front vertical edge of the barrel ring. If the bolt hole is drilled too far to the rear the scope mount rear end may contact the receiver stripper clip guide dovetail. This lifts the back of the mount so the mount horizontal key doesn't fully seat in the receiver horizontal groove. Consequently, the mount is moved left, right, or down at the front end. The rifle is then likely to shoot high or to one side. Additionally, some bolt holes are undersized due to worn out reamers or not drilled perfectly perpendicular to the receiver wall. A very few commercial receivers lack the scope mount recoil lug or bolt hole.
Receiver Horizontal Groove - The height, angle and width of the horizontal groove affect the fit of side three point scope mounts to M14 type receivers. Some commercial receivers have horizontal grooves too shallow and narrow to accommodate military specification mounts such as the Brookfield Precision Tool and Sadlak Industries models. The USGI drawing number 7790189 specification for the horizontal groove is 0.149 " to 0.153 ” wide at the top of the groove with a sixty degree angle from the bottom of the groove. The bottom of the horizontal groove should be 0.070 ” to 0.078 ” wide. Commercial receiver horizontal grooves can measure as narrow as 0.120 " at the top of the groove.

 

[Pietro Beretta]

I had mine installed by my gunsmith, and its set perfectly!

 

[Holleyman]

Oh boy, I had some problems with my #18, My drift was the opposite of yours. Having said that, you need to look at different things first.

There is a post about mounts that is stikied.
First you need to look for contact points between the rail and the receiver. It may be touching on the top or front edge of your receiver.
Also it may be touching the stripper clip mount.
When installing it don't put the stripper clip mount piece in and backoff the front pad, look for any contact points, the mount should only touch the vertical & horizontal keys. Use some soft clay between the mount and receiver when installing to see if clearence exists.

Also look to see if the mounting hole is centered with the vertical key slot, mine has a slight offset, you may have an issue with the slot not allowing the screw to center itself thus causing drift.

Get back to see progress

taken from http://www.canadiangunnutz.com/forum/showthread.php?t=35091

Thanks a ton! I had to do a bit of filing on the rear of the mount to get it to install without binding back there and dremel a taper on the rear of the slot iinsert to match the taper of the horizontal slot in the receiver. Would help a lot if the mount actually came with some installation instructions! I bore sighted it this morning and range tested it this afternoon. I am in awe at the accuracy of this little $400 rifle. I shot 40 rounds (4 groups of 5 just to zero the scope at 100 yards) and 4 groups to test the rifle. Two of my groups shot around the 1.5" -2" mark with surplus ammo.

Again, thanks for the help. I would have never found that info in here with the poor search functionality of this site.