I'm thinking along the lines of a little slingshot-pistol, pocketable (15 cm long?) , shooting special projectiles built for the sole reason of smashing flies. I already designed those in my head: A wooden dowel, about 10 mm diameter, about 100 mm long. In the front of it you attach a round piece of thick (1mm) leather with a screw. On top of that you glue a equally big, but thicker, piece of foam. That way it won't damage any walls it might hit. The pistol can in that case be no bigger than 10 cm from front of trigger to back of triggermechanism, in order to fit with the bolt. The hardest thing with this build is to make it look good- I usually dont make good-looking things. (Just look at my crossbowpistol to see an example of ugly craftmanship) But as I said, I want this to look really good! I will try to upload a quick sketch I made this morning.