Surely Sinistar will deliver! D:
And I shall!
Raise the banners, sound the battle-horns, form the ranks! 3, 2, 1 - Deeeeeliiiivvvvveraaaaanncccceeeee!!
Pompous intro aside, I apologize for not doing that earlier. But my HDD got bust last Sunday so my internet capabilities were severely limited.
"But but Sinistar, you were online since last Friday!" I hear you say. "Why did you neglect your duties? Were you too busy fappin or something?" And to that I'll answer that I didn't post earlier because shut up.ANYWAYS:
So, you are basically making a home-made battle drone that'll spew plastic death from above upon unsuspecting scum of the society? Or something along those lines. Well, my best guess is you'll need something custom made. By you. So, you'll need something like
this or
this or... any
fully automatic airsoft pistol, I guess. Now, tbh, pistols aren't my specialty. Never advanced to the point I'd buy myself one (even though I had quite some on my to-buy list, hehe). That means I never opened one myself and never really saw others do it. But AEPs basically shouldn't be that different from AEGs - both should have an electric motor and gearbox. To minimize the weight, you'd thus discard the housing of one such pistol and be left with above parts and, of course, barrel. Dunno what your copter's setup is, but I'm guessing arranging said parts and also a battery would now be much easier than fiddling around with a bulky pistol.
One immediate problem I see now is bb supply. You already said you desire a big capacity and hi-cap pistol mags can't match with those of rifles. BUT. The stripping of the gun gives us yet another benefit - the gun's housing is not a limit for your mags anymore, huzzah! So theoretically you could strap on one of those drum mags I was rambling about above. Of course, the bigger the mag, the heavier. You'll have to work it out yourself what's the most effective one for your case.
Still, the problem of connecting the supply to the shooting mechanism remains. But what you really have to do is just find a PVC pipe of right diameter and connect them airtight. Actually, thinking now, flamethrower project mentioned above seems like something whose you could use. Maybe NAV can throw some suggestions?
Do note I'm talking purely theoretically here. I'm making a mental sketch that says this might work, but imagination is a fiddly thing. You could just strap a pistol on your copter and be done with it. But you'd still have to connect the trigger somehow and that, again would probably be a lot easier without the housing.
Or you could do the same with a stripped-down rifle, but pistol would definitely be better when it comes to wight. If you do go the pistol route however, I'd wager you could get just gearbox + motors even cheaper somewhere as spare parts.
Also, there's that whole question of HOW to fix those parts on the copter. Gearbox and motor must be fixed really tight, no wiggling about there. But I have no more suggestions for now.
Anyways, keep us updated! Oh, and if you by any chance get arrested because it turns out you really want just an assassin drone to take care of some hated politician AND your project was in fact successful - please don't tell them any of us helped you. Blame it all on the voices in your head, that usually works.