Airsoft, although safer, should still be treated with similar respect as a firearm. They can cause harm to yourself and to others if not used properly. Only those who are responsible and have good intentions should be allowed to participate in anything involving airsoft.
I have spent many years researching, designing, building and testing many forms of pneumatic projectiles including airsoft and spudguns. I am no expert, but I do know my way around the block.
with that said....
The following will show my latest creation.
Step 1: The Pneumatic System
All pneumatic fittings and valves used are machined in a factory, are made of brass, steel, aluminum etc, and are rated well above what they are operated at.
This gun works by:
1. charging a main tank to a high pressure, I have used 120psi thus far and have no need to go higher just yet
2. operation of a direction control valve (3 way valve, 2 position) (trigger) empties a small portion on the main tank to a secondary holding unit
3. This secondary tank holds the same pressure as the main tank, however holds less volume, just enough to project the bb
4. A quick exhaust valve is operated, via the direction control valve, to empty the secondary tank through the barrel
The only modifications done are to make the operation of components easier mechanically and to integrate into the gun.
Step 2: Other Parts
The barrel is a 3 ft section of 6mm stainless steel tubing.
The barrel is housed by a 1/2" section of PVC for strength and protection.
I added a cover for the secondary tank to protect it and make the gun more sleek
I have sights intstalled
I have a homemade bipod
I have a toy silencer that actually improves range (haha, does not make it quieter at all)
The best part of homemade projects is that there are no rules. I used parts I had laying around and made what comfortably fit my shooting style. I wont get into any more specifics, because you can do whatever you please.
Step 3: Finale
There are many ways to make it more efficient as a bolt action, with an actuator I can easily make it semi automatic, and with some springs in the right place I could make it full auto.
This is the final product disassembled and fully assembled. This was a fun project that has taught me a lot. It was a great building block and has yielded great results. I estimate 300fps at 120psi. When the tank is filled at 120psi I get about 5 powerful shots before a drastic drop in performance at lower pressure. With my rig I can switch out the tank for a higher one and can operate with regulated CO2.
This does draw blood as is, so be forewarned, this is not a toy, and should be handled with care.
I do not take responsibility for carelessness and lack of common sense. Before undergoing such a project take the time to research the systems you are trying to mimic and the parts you are going to use.
Be safe, have fun