I built this marble shooting airgun after being inspired by Matthias Wandel's marble shooting airgun. I wanted to build my own but instead of making it a muzzle loader, I wanted mine to be a bolt action. I also wanted it to be a wadless design. I built it to be able to handle 200PSI but I have not yet fired it at anything above about 80PSI yet. I used a stainless steel Schedule 10 pipe as the barrel and used o-rings to both seal the bolt and retain the marble before firing. I used a ball valve with a spring and parts of a door latch to build the trigger mechanism. Part of my goal was to make it completely from parts that would be available at any regular Home Depot store. With the exception of the barrel, I was able to do so. One thing that I considered during the planning phase was to swap the stainless steel barrel and use a schedule 80 pvc barrel and use 50cal muzzle loads as the ammo. Anyway here are some pics of the finished airgun. As with any posting of a potentially dangerous project like this, the pictures are for entertainment purposes only. I do not offer any advice or instructions on building your own. If you are not capable of figuring it out from the photos, you probably should not be be building one.
I finally got around to building version 2.0 of the Marble Shooting Airgun. Much of it is based on the original design with the exception of the ball valve and door latch trigger mechanism have now both been replaced with a 3/4" automatic sprinkler valve that has been modified for blow gun operation. Of course the blow gun has been positioned so that it is in the right trigger position. It's hard to see in the pictures, but I ported the sides of the blowgun since I used the nozzle to help mount the blowgun. The idea of modifying or "turbo charging" the sprinkler valve came from Doom Labs. Although their site contains a lot of really useful information, it is impossible to point people directly to it since they monkey with the URLs.
I used my Bicycle pump to get the chamber up to 160psi which it held although it was leaking. The whole system started leaking at about 80psi, but I could never find the source of the leak. It sounded as though it might have been leaking at both the bicycle pump and maybe at the sprinkler valve, which is not surprising since both are rated to only about 100psi or so.
The airgun shoots very nicely. Without a chronograph I have no real way of testing the muzzle velocity, but it appears to exceed my paintball marker which was chronographed at 280fps. I rigged up a foam block backstop using some leftover 1.5" insulation foam. I used 3 layers making it 4.5" thick backed with a 3/4" piece of particle board. Regular marbles fired at 25 feet and 160psi at the backstop will completely penetrate all 4.5" of foam and will severely indent the board and cause cracks on the backside. Using 5/8" steel balls, the particle board just barely keeps the balls from going all the way through the board. I have been tempted to put things in front of the backstop to see what it will do, but am afraid that a ricochet will cause serious bodily harm so I haven't tried it yet. The accuracy seems good, but I haven't had a chance to fire more than about a dozen shots or so since building it, so the accuracy is more or less untested at this point. I plan on making a sight which will help with future testing.
A local paintball field let me borrow their chronograph to test the airgun. Using a marble and about 160psi I was getting just shy of 400 feet per second. With the 5/8" steel bearings I was getting just over 250 feet per second at 160psi. The marbles are about 1/3 the weight of the steel bearings, but because they are slightly smaller they have more blowby. The limiting factor is clearly the amount of blowby that slips by the marble as it travels down the barrel. I am quite pleased with these results. I know they could be better if I used a wad, but my goal was to make a wad less design and being able to put marbles through 3/4" thick particle board is still pretty impressive. According to Matthias Wandel's marble shooting musket page, Canadian Firearms laws say that anything that shoots over 500 fps is considered a firearm, and both of us were able to get 400 fps pretty consistently. I have no idea what the laws are here in the United States but I am not terribly interested in contacting them to find out. Given another chance I might try a few wadded shots to see if I can get better results but that would take another opportunity at a chronograph.
As before, these pictures are for entertainment purposes only. I offer no advice on how to build your own and these are certainly not instructions on how to go out and build your own. If you should attempt to do so and in the process do something illegal, or injure yourself or someone else you have no one to blame but yourself. Imagine the most airtight disclaimer you can, add in a safety factor of 10, and you might begin to approach the disclaimer I am attempting to make here. Whatever happens, it will not be my fault. Clear?