Check this gun out

[MarkL]

Some of the math in that article doesn't quite add up. Consider this little nugget.

"Unlike conventional weapons that deliver a bullet to the target in intervals of about 180 feet, the DREAD's rounds will arrive only 30 thousandths of an inch apart (1/32nd of an inch apart), thereby presenting substantially more mass to the target in much less time than previously possible."

By my calculations, using the other data given in the article (120,000 rounds/min at 8,000 feet/sec), the rounds would be four feet apart, not 0.030 inches.

It might also be fun to calculate the power requirements. First you need the mass of one .50 or .308 steel sphere, then calculate the kinetic energy it would have at 8000 fps, then multiply by 2000 rounds/sec to get the energy required per sec, then convert to kilowatts. I'm betting the electrical generator you'd need would be a lot bigger than the 28 pound gun.