SpudFiles

Yep, that little valve will allow me to charge semi-automatically

Have you calculated the volume of your balast chamber and barrel? What I have found is about 1.5 times barrel volume for balast chamber works well. You have more than 3 times your barrel. I figure you have just 2 shots from 1 HPA tank of that size if it will also be regulated down to 90psi like your compressor option.
I don't know of any regulating 3-way valve that will represent what you have as a "T" fitting in your picture. Just curious, how are you going to build and actuate these valves from inside the pressurized chamber?

Okay, few more revisions made, found a way to make that valve. although it isn't as compact as before.

will post revisions as soon as possible.

Hurry up every chance you get. But remember to stay within your design parameters.