I machined my vortex block from a 2 inch rod of Nylon, to fit in a 1 3/4 pvc pipe. The goal of this first test is to get the gun as small as possible so I can later fit the thing inside realistic airsoft bodies.
Here it is with an airsoft barrel threaded 3/8 fine and screwed into the block:

I used a steel ball and spring with a grub screw to adjust spring tension to act as a hop up and to keep bb's from rolling out the barrel when not firing:

This is a shot of the end cap with 2 O-Rings to keep the chamber sealed:

I am using a spring and plunger to keep the BB's pushed towards the vortex block:

I am also using the barrel as a guide rod for the spring and plunger:

All the major pieces, the PVC says it is rated for 330 psi on the side, I am using 100 psi for all the testing:

Here it is assembled, it holds about 4000 airsoft bb's, I am using 0.25 gram madbull bb's for the testing:



To make it portable I am testing it on CO2 with a Palmers rig from another project:

With 100 psi I am hitting 83 rounds per second so far:
