Bible -
Interesting, and looks well designed...but.
And yeah, while nicely done, it won't work using the current GK1 as the gun !
The GK1's fill socket is on the wrong end of the cylinder / printed frame ! The printed frame is also too short for the current gun. And possibly other changes required.
Do a redesign / refit, and lets see what happens. Keep the overall height from the top of the shroud (barrel) to the bottom of the cylinder, as short as possible to reduce the "blocky" look.
Mike