Here's my current work in progress: (sorry about the shitty picture. I will definitely take better pictures when I finish it / am happy with it)

It definitely one of the biggest homemades ever made, if not the biggest (definitely not a product of practicallity, though) It has a 4" PVC Plunger Tube, which is currently manual, but I plan on adding bungees and a large catch mech to make it a semi-springer (semi because it'd be bungees rather than a spring)
It has eight 2.5' long steel barrels that are capable of flinging 5-10 tagger darts at a time with ranges up to (hopefully) 100' angled. I say hopefully because I have not fully range tested it yet, but I do know that it is capable of 30' flat at least, testing it indoors. (I expect the bungee upgrade to drastically increase performance)
The turret is fully removable, but it's definitely not coming off unless you want it to. I left it open for better turret designs that may come to me later on.
I have also made a base for it, which can swivel 360 degrees and move a little vertically. (There's obviously no way in hell anyone is carrying this thing, it's at least 5' long and over 20 pounds)
The turret is manually rotated, with a brass breech that is inserted into the barrel for a better seal. It only takes about 3 seconds to move to the next barrel, so the rate of fire is decent (about one blast every 5-10 seconds)
And before I get any flames for spending way too much money on a retardedly huge and impractical gun - I don't give a shit, keep it to yourself. I know this thing is an awkward clusterfuck - that's the fun of it. I'm making it because I can, and because it's fun. Maybe it'll turn into something more practical later, maybe not. At the very least, I enjoyed building it.