Actually, over the past year or so, I've read in numerous forums that the ARMS mount sometimes works and sometimes does not work on the SA rifles. However, the ARMS mount works fine on the Poly (mine included) LRB and Norinco. Check over at the M14 forum and you'll eventually find it.
http://www.ambackforum.com/viewforum.php?f=108&sid=5168e91389cb7f4b8380bff785a84e3d
and here specifically. Scroll down a few posts and you'll see the SA/ARMS18 mount issue.
http://www.ambackforum.com/viewtopic.php?t=26636&highlight=scope+mount+arms+18
There's something about the way the SA receivers are milled that causes the brass to catch in the space between the mount and the receiver. This is not an issue on the Poly, however. The other mount mentioned here will evidentally work, however.
Rome