Building a BB Machine Gun
Owning a full auto gun in most countries is either illegal or nearly impossible to acquire. Fortunately for us, we can build a air powered machinegun very easily and have loads of fun tearing up targets. This particular type is sometimes called a cloud machinegun. They are simple to make, but will run through a lot of air and ammunition.
What you need:
It really doesnt take much to build one. Here's what I used:
* 1/2" npt brass pipe nipple 2" to 4" long - ammo chamber
* 1/2" brass cap - closes the chamber
* 1/2" brass coupler - to join the ammo tube to the barrel adaptor
* 1/2" to 1/4" brass bushing - reduces the fittings to fit the barrel
* A barrel, you can use a 1/8" pipe nipple or length of brake line
* Various 1/4" brass fittings such as close nipples and 90 degree fittings
Tools and Supplies:
I used a drill press and 1/4" npt pipe tap. A wrench and vicegrips as well as some thread tape come in handy too. For ammo, this project can use airsoft ammo or 1/4" steel ball bearings (commonly sold as slingshot ammo).
Putting it together
Check out the picture above to see how this thing is put together. Use thread tape on one side of the ammo chamber. Attach it to the 1/2" coupler. Use thread tape on the 1/2" to 1/4" brass bushing and attach it to the other side of the 1/2" coupler. Now, clamp this assembly into your drill press vice and drill and tap a 1/4" npt hole into the side of the coupler. This is where the air enters. You can attach a 90 degree fitting and quick disconnect here as shown in the picture to hook it to an air compressor. We are about 5 minutes away from full auto action.
To complete as pictured above, use a 1/4" to 1/8" brass bushing to attach a 6" 1/8" npt brass nipple. This will be the barrel. Once the barrel is attached, you can load the ammo chamber with airsoft ammo, then cap it off with your 1/2" brass cap. To fire, simply connect the quick disconnect to your air compressor or portable air tank. It will dump the ammo out at an impressive rate of speed. Here's a video that shows how well this simple BB machinegun works:
Pretty impressive for something 10" long that took less than 10 minutes to build. This airgun is ugly as homemade sin and is in bad need of improvement. You can improve efficiency by using a longer barrel made from brake line. Using PVC, you can put together a nice shroud and make it look more like a gun. A ball valve allows you to control firing much better than connecting and disconnecting a hose. Switching from airsoft to steel ball bearings gives you more shredding power. Here's what it looked like when I modded the basic thing you see above:
Looks much better and works better too. Here's a video of it:
This thing uses a lot of air, so you'll want a good sized air compressor or regulated CO2 bottle to feed it. I personally have a small 4 gallon compressor. To feed my machinegun, I connected a 7 gallon portable tank up to my compressor using a homemade hose, thus making a 11 gallon system. Your compressor will have to work a bit harder, so you will want to allow it to cool down after it fills the two tanks. Uses tons of ammo too, so have a good backstop that allows you to reuse your ammo. You can use different materials for the barrel to shoot steel BBs as well. With some creativity, you can come up with a pretty cool airgun that is highly addictive to shoot. Be extra careful with these, while one shot isnt the most powerful in the world, these do have a sand blasting effect that can prove quite devastating.