OK... looking at your feed, it's impossible. Sorry, wouldn't work. The gear to pull the bullets out would likely be too close together, and the chambers almost certainly would be to close together to be safe.
I had figured on each chamber being about 3 bullet widths apart. Like this:
1-0-0-0-2-0-0-0-3 Gun chambers (0 being being space)
That allows plenty of operating room.
How much range would you think this thing should have? Its accuracy is going to be HORRIBLE if it is fired without a support.
If you really just need to put swarms of projectiles in the air really quick, at shorter ranges, get an auto shotgun. It's a lot more practical, and you won't shoot the rifling out of the barrel either. And an auto-seared Saiga 12 with a 20+ round drum, loaded up with flechette sabots, definitely has a lot of lethality, range about like an SMG, and puts a lot of projectiles in the air in a hurry.
As for calibers, you seem to have little comprehension of the difference between pistol cartridges and rifle cartridges and just how significant the gap is.
A person convinced that the ends justify the memes.