I bought a #39 A.R.M.S. to mount my COMP-M. I noticed right away the Aimpoint was off to the right about 2mm.

I discovered the #39 was at fault. The scallop in the clamping arm that grabs the front of the handguard is machined off center.

My guess is they do this to force the mount to one side thereby taking up any clearance between the mount and the carry handle slot.

Seems like a good idea but I also noticed the mount shifts as I vary the torque applied to the thumb screw holding the clamping arm.

With sufficient torque the mount reaches maximum deflection and always lands in the same spot.

The problem is the forward end of the mount is 2mm off center.

My plan is to re-machine the clamping arm so the scallop is on center and build tapers onto the part of the mount that sits in the handguard slot to take up any excess clearance.

Anyone found a better solution?

I would send it back. That way the finish is intact and they are aware of a quality control problem.

-elliott

Send it back.  Elliott has the correct fix.  Get a new one.  Now if was a cheap knockoff that would be a different story.

It doesn't look like a manufacturing defect. I think it's intentional. I wrote Atlantic Research just to make sure. I'll post whatever I find out.

ARMS had some quality control problems recently but I heard those got ironed out. You may have gotten one that was sitting on a shelf for awhile before you bought it. Send it back.