

This design is similar to most homemade airguns, and as such, the firing mech can be replaced with whichever sort of release mechanism desired, PVAT, Ball valve, WNTS, etc. Anything that isn't backpressure.
It works much like Kane's 7-11, compressing air "in the pump", and does not have a secondary tank that stores pressure.
The front nodule is the trigger, and is connected to the backwards check valve in the pump via steel rod. Depressing the front button is how you fire the blaster.

A visualization of how the blaster works. "Snapshot" taken at moment of firing, red is pressurized.
Materials
2" PVC
Caulk gun [large]
2" piston cup 9411K14 [Can be substituted with anything that has a 100% seal]
Firing mech of some kind [I used a check valve system]
2" to 3/4" PVC reducer bushing
3/4" PVC
Washers, nuts, and bolts.

Pic of the piston cup
The main body is just a piece of 2" pvc and the bushing couplered together.
If you havent noticed yet, I forgot to take pictures during assembly, but the whole thing is pretty simple.
Questions/Comments/Flames appreciated.