The 9mm Metal Storm has been around for a few years, DSTO in Oz reviewed it early '99. Max rate of fire is *very* fast, the six-barrel prototype managed 180 rds in 0.01 sec --- yes siree bubba -- that's 1,080,000 rpm.
more details at:
http://www.sciam.com/1999/0499issue/0499techbus2.html
-ric
more details at:
http://www.sciam.com/1999/0499issue/0499techbus2.html
-ric