Buddy of mine did the special effects for Scarface.
He had to create a "machine gun" that shot ball bearings to get the effects they were looking for, so had this home made, C02 tank powered "rifle" with a hopper that held 500 ball bearings at a time, cycled at 700rpm and shot the bearings fast enough to break glass and make holes in drywall etc.
To say shooting it was fun is an understatement of the century. (And with a electro magnet, or just a plastic cup, you could use a regular magnet to pick up the bearings, and shoot them many times over.) He made up an electro magnet on a stick that would allow the crew to "mop up" the bearings and then dump them back into the hopper, or another container with just the flip of a switch.