I normally don't make concept guns, but I decided to see if this one mech I thought up would work. It works by having a ratcheted elastic powering a rotating firing pin. It all worked out on paper, but when actual building came around; this gun failed to shoot. But I was satisfied that the mech was possible, and functioned at all. I did take pics of the "completed" gun for you all to see.
This gun on paper would have shot 25ft at about 300-500 rpm at an estimate.
Now for the pics of the gun below.