The Military has used two that I know of for sure.
The Brookfield Precision mount is probably the best M-14 mount around.Sadly, it is no longer made, but Smith Enterprises makes a copy of it.
The other mount is the A.R.M.S. #18 mount.There are two styles.The older style has a two section rail, and the newer one has a full length rail.
If you are short on funds, you can fing a Springfield Armory 3rd Generation mount pretty cheap.They are ok mounts, but theabove two are the best ones out ther right now.
SKBY.