From: Bart Bobbitt <bartb@hpfcmgw.fc.hp.com>
Subject: Weighted Magazines

Several years in California, an M1A shooter with magazines weighted with
shot had a slam fire.  The energy released was enough to destroy the
magazine and dislodge the shot.  He had a whole bunch of wounds on his
body after all those pellets came out and hit him.

So, I don't recommend adding shot to an M1A magazine; it can be like
micro-grape shot if a slamfire occurs.