Not sure if this has been discussed before, but here is an idea that was tested and found wanting, a 1,200 barrel shotgun bolted to the front of a Huey:
https://medium.com/war-is-boring/the-u-s-army-tested-a-helicopter-shotgun-armed-with-1-200-barrels-ce1ca126537d
Interesting read.
The clickbait link to the 10,000 rpm "Microgun" is also interesting.
Reminds me of the more recent "Metal Storm" guns? These can reach a 16.000 rounds per second, but it's rather a dense, single blast of slugs than true continuous fire.
http://en.wikipedia.org/wiki/Metal_Storm
Great read, thanks ! Allsorts of interesting links at the bottom as well.
:cheers: