Step 2: Naming conventions
The barrel, Stock and Handle are fairly standard gun parts so I'm on safe ground there.
The front of the gun has a stuck out bit which looks like the pilot flame for a flamethrower. I call this the spark generator (not to be confused with Sparc International mind you!)
The nobbly bit reminds me of the high voltage electricity stuff, so I call this the cascade tower.
The bottle on top of that I call a reservoir, conveniently placed to slowly drip stuff into the tower.
The bottom cylinder is below the gun so presumable injects stuff upwards, hence becomes the injector.
Finally the large cylinder on the back of the weapon reminds me of a power cell.