"Holy shit!", I exclaimed after pulling the trigger and watching a nail infused Nerf dart engage warp speed across my garage and bury itself into a hunk of 2x4. This was my reaction after the initial test firing of my then newly constructed PVC air gun. I was genuinely surprised that a lowly 30 psi of air pressure contained so much energy and that the overall contraption worked so well.
I came up with this idea after discovering from some fellow Youtubers that a suction cup style Nerf dart fits quite nicely inside a 1/2 inch PVC pipe. The rubber suction cup end fits just well enough to form a decent seal inside the pipe but loose enough that you can use your lung power to blow the dart very effectively. If you push a medium sized nail through the rear hole of the Nerf dart and poke it through and out the rubber suction cup, then you have a decent blow dart gun for next to nothing.
If lung power is good, then a compressed air tank would be better right? Believing so, I got out the graph paper and started designing my gun. One of the most critical parts needed for the gun was the air release mechanism. I really wanted an electric valve of some sort - I imagined a mechanical valve would be too slow (thus reducing projectile velocity) and introduce unwanted movement which would effect accuracy. Again some enterprising Youtubers came to the rescue - a sprinkler valve from the local hardware store would do just fine.
Now the valve needed a battery and a trigger, and the gun needed a grip of some sort. As it turned out I had all of these items in the form of an old Ryobi drill that I no longer needed. I ripped the motor assembly out of the drill body and enlarged the resulting cavity to fit tightly around the intermediate pipe of the gun. Wiring the sprinkler valve to the trigger of the drill allowed the battery to power the valve for a near instantaneous release of all the air pressurized within the 4x12 inch reservoir attached to the rear of the gun.
I already knew that i needed a 1/2 inch diameter PVC pipe for a barrel, the length however was a design parameter that required some trial and error to get figured out. Judging from some of the comments on the video, the ideal length is much longer than you might think. While I did not scientifically verify with a chronometer, my seat of the pants meter told me around a 5 foot barrel length was the ideal compromise between maximum velocity and structural integrity. With this setup the projectile seems to want a relatively long barrel to get up to speed. Shorter barrels seemed to spit out the projectile before all the air had a chance to go to work.
This fairly simple design, capable of 100+ psi, propels Nerf darts at scary fast speeds - we're talking welt leaving speeds as seen here :
If you want to try this project yourself you can order one of the sprinkler valves here from Amazon.
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