Gunnit Rust: "Strike Triggered Ballistic Device" - a pocket pneumatic boltgun

I threw this together using a mixture of over-the-counter Home Depot brass fittings and some custom machined parts. Basically a pneumatic device that projects a hardened steel bolt driven by 850 psi of compressed air, which can be triggered by using the device to strike the target material, what can be described as an air driven powerhead.

The working principle is fairly basic, a piston pushing on the bolt that is held in place with a ball detent, just like a quick coupling. Moving the collar - either by pulling it back or by striking the whole thing against a target - displaces the balls and frees the projectile, allowing the air pressure to push it out. The bolt is a 0.3" diameter high speed steel rod that weighs just over an ounce, and the piston which shoots it out has over 200 lbs of force acting on it. I also made a higher velocity projectile weighing around 1/4 oz which the chrony clocked at just under 200 feet per second.

Imgur album

youtube video of initial testing

youtube video of lighter projectile including 10% gelatin test

edit: thank you all for the feedback, appreciated