First post is the Joe pseudo FLAK cannon.
For reference, here is the plasma drill:

And here is my Joe version (I need a new camera; images aren't the best):




It's a tight fit but you can get a 6" figure in there. I'm planning making a bunch of different versions like one Cobra and different lines. Black Series Empire, Marvel Legends Hydra, A.I.M., Stark Industries, SHIELD. Blasting Xenomorphs.
The barrel is made from a water brush and can be taken apart and configured differently.
Thanks for checking out my stuff.