As far as locking on the rail, assuming it slides on completely and it isn't tight enough you can remove the lever C clip, remove the lever, turn the screw so it will be tighter, and then re-install the lever so it will be snug/secure when tightened to the "fest" position. Do not over-tighten it nor is it advisable to close to the lever to "fest" when off the rifle else you may crack the mount (repro or original). If it simply won't go all the way on then you have to file the repro mount inside the dovetail cutout with a proper 3 point file. If that's the case it's best to remove the rail release button/lever (the push in lever) altogether else you'll file the "fingers" that catch on the rail notch.