Academic weapon graduation gift

I made this little stickman as a gift for a friend who had graduated university. I essentially wanted to design something that embodies the word ''academic weapon'', so I came up with a very simple spring loaded mechanism that transforms a bookcase into a tiny gun when you press down on the academic hat. The compression spring I used in my design was 7 mm in diameter and 12 mm in length. I don't know the exact spring stiffness, but I recommend choosing a spring that isn't too stiff, since the only purpose of the spring is to push back the academic hat when it is released.

I started by smoothing down the pins on Stickman_back_1 with 120-grit sandpaper so the two halves of the stickman fit smoothly and firmly into eachother. I noticed that there was a very noticable gap between the two dissected parts, so I filled the gap with a putty-like mixture of wood filler and acetone. Keep in mind that acetone evaporates quickly, so you'd have to be quick when applying the mixture. After filling