Questions about a small pump-up gun

[Gusher]

Please go easy on me here. I have made a couple of air cannons in the past and used them at several indoor football games shooting tee shirts. The guns I have made are big and I use a SCBA (like SCUBA) tank as my air supply. My question is how should I go about building a smaller one that I can still shoot shirts with a 3" barrel that I pump-up?
What is the best hand pumps you have used?
Should there be a check valve between the pump and the chamber?
I have never made a mod. valve would that help with this smaller run to achieve better results?
Thank you in advance for the help.

[Novacastrian]

A modded valve will help performance however to make a cannon that shoots t-shirts any kind of distance and is pumped up by hand is kind of crazy i think. Your arms will fall off after about 2 launches i think.
You could use a stirrup pump or a MTB pump, but i recommend sticking with the SCBA tank, or get yourself a "pony" bottle used for diving.

Edit: Welcome to Spudfiles "Gusher" What a funny name, you don't want to hear that word on the operating table, "Nurse, we have a Gusher!"

[Hubb]

Have you considered using 12g CO2? It will be fairly easy to incorporate into a T-shirt launcher.

Going smaller with the size means the pressure has to be increased to get any type of performance and a 12g will allow for that, although you may not be able to use a sprinkler valve.

If you insist on a hand pump, I would suggest a shock pump...to keep your arm from falling off after the second or third shot.

[Novacastrian]

Mr hubb, a shock pump only displaces a very small amount, how will that save his arms? Good idea with the Co2 though

[BigJon]

Yeah if you tried to use a shock pump, you wouldn't get very many shots off as it is very tiring. Try to look for a bicycle pump or something similar that puts out large volumes of air.

[Hubb]

I apologize for not being clear. I was under the impression that he waned a smaller chamber, which is why I recommended the shock pump and 12g setup.

[Gusher]

Sorry not playing dumb it comes natural what is a shock pump?

[ShowNoMercy]

A pump that is used to pump shocks.

[Gusher]

If I use a 20oz. CO2 bottle how many shots should you get?

[JDP12]

depends on chamber volume, and what pressure you want to operate at

[Gusher]

On my other guns I used a 2 1/2 lb extinguisher as a chamber at 120psi.

[Hubb]

If I use a 20oz. CO2 bottle how many shots should you get?

Use this.