Kimberfan:
I've got an M1A Scout 18" rifle wearing an ARMS #18 mount, Leupold QRW rings and a Leupold FX-2 4x33 scope. On the scope I currently have one Stoney Point elevation knob for easy distance adjustments, and at some point this summer it will get a second one for windage.
The best groups I've shot with this rifle were 1.25", from a bench, using 168gr Hornady HPBT match handloads. Typical groups with 150gr surplus grade ammo run about 2-2.5" from a bench or 3" from prone.
I did have the ARMS #18 rattle loose on an exceptionally rocky and bumpy jeep ride last year during elk season, and I removed it to complete the hunt, relying upon the iron sights instead.
Locktite is your friend with this mount. Apply it to the rear clip-guide mount as well as the receiver screw. Make sure that the front elevation adjustment is well down against the top of the receiver, and that the locator ridge on the side of the receiver lines up properly during assembly.
Also: remove the spring from the front elevation adjustment screw. Invert the concave washer so it provides for a fixed degree of elevation, screw in the elevation adjustment screw further, so that the mount cannot bounce and by bouncing, flex the tightness of the rear clip-guide mount and thereby loosen it.
I can remove the bolt from my rifle without removing the scope mount.
I just re-installed the mount about 3 weeks ago and re-sighted in. I'm still testing for tightness or any loosening after installation, but it seems fine. In about 150 rounds, I've had 2 stoppages by empty cartridges impeding the rotation of the bolt or forward motion of the op rod. I will be having my mount modified to remedy this problem.
If I cannot have the extraction/ejection problem fixed and the mount installed in a reliable way where it doesn't shake off from rough use, I won't keep it on the rifle.