Re: M1A SCOPE MOUNTS
Biggest problem I've seen with mounts is a too-big horizontal lug on the bottom, which does not adequately grip the corresponding groove in the receiver.
That leaves the vertical lug, closer to the axis and MUCH smaller, as the primary part resisting recoil. A side-screw rear mount (as compared to a clip guide that set-screws into the dovetail) has enough slop that it does not resist recoil torque on the mount. That's why so many people have trouble with the Springfield Armory 3rd-Gen scope mounts.
I have a 1980s-vintage of fundamentally the same design that came with my Leatherwood ART-MPC. Its horizontal lug is much narrower, and the rear side-screw is far enough back that you can drill and tap a standard strip clip guide. The rear screw only stabilizes the thing for windage. The vertical lug also has a steel set screw in there, which flattens its sides into the receiver groove and provides, IMO, a much more secure backup to resisting recoil torque. Unlike the SA 3rd-Gen, however, it does NOT have groove on the bottom side to allow use of iron sights. Gotta find a machinist to mill that for me.