The only real 'machine gun' add-on I've liked over the history of Blockland was Sniff's weapons. I didn't even like them that much, though. But they were better than the rest, seeing as how you could tell SOME difference between the functions, and a large difference in the models.
Then again, they were loud, annoying, and easily abused. :(
I probably shouldn't go on a rant about them. You've basically said all I had in my head and then some.