I use the Sadlak Airborne steel mount and have put it on three M1As; a standard model, a loaded model, and a SOCOM. They covered the years since 1980 and the mount fit them all perfectly, without any special modifications. The trick is to tighten the screws in a Round-Robbin fashion and wiggle the mount as you go. I also use small levels to verify proper alignment with the centerline of the bore as I tighten the mount.
I'm not a gunsmith but since I have installed this particular model mount several times I have noticed that I get the best results by using the following process.
- Clean the screw hole that is in the side of the receiver. I chase the threads with a tap and then make sure that the threads are clean and dry.
- Make sure that the dove tail where the stripper clip guide used to be is clean and dry and has no burrs.
- Install the wedge that goes in to the dove tail, without tightening it.
- Install the mount and loosely tighten the side screw.
- Make sure that the front screw does not touch the receiver ring.
- Tighten the side screw, with the tensioner at 12 O'clock, and the single large allen screw in the wedge slowly by hand until they are all snubbed up but not torqued. At this point you have gotten the mount pretty well aligned with the slots on the side of the receiver and the wedge isn't torquing the mount to either side.
- Tighten the small wedge screws that fix the wedge to the receiver.
- Torque everything to spec. That tensioner under the side screw will push the mount left or right so it can be used to help align the centerline of the mount.
- The last thing to do is tighten the screw up front. Adjust it so that it just barely touches the receiver ring. This screw can help align the mount fore and aft but remember, this screw isn't meant to be a used like a jack screw, it's used as sort of a tension device. You don't want to bend the mount with it so if you use it to adjust that angle of the mount then it would be best to loosen the other screws just a bit and then re-torque everything to ensure that nothing is being twisted or bent by the screw pressure.
I also do all of this while checking the alignment of the mount using two small bubble levels; one level I put on the receiver and the other on the mount. I compare the two and make sure that their bubbles match. Check for level fore to aft and side to side.
My method is a little slow but, knock on wood, I usually only have to fire about two or three rounds at 25 yards, a couple at 50 yards and then one or two at 100 yards and I'm dead on. And I don't have to use all of my adjustment range to get on target, just a few clicks one way or another.