It has to be a pistol, and it has to be small of course. I settled for arrows as those can be poisoned and are therefore potentially lethal, even without great power. But if course it has to be powerful enough - not so easy with such a short draw length!
So I settled for the smallest arrow shooter I ever came up with, and did a few sketches. This is also a good example how my "blueprints" usually look like - I am really not a very good engineer.
This makes a perfect "barrel" without the next-to-impossible task to drill a straight hole through the entire weapon.
After everything was functional, I made the cocking device - a fork that you push in from the muzzle, then you lean against a wall and press forward until the sear engages.
It is also very very accurate - thanks to the barrel that guides it perfectly well.