SpudFiles

Hello, my name is Jason.
I have built two pneumatic cannons before, and airsoft regularly.
I have been airsofting for two+ years at fields and events, and want to build a BBMG to field.
Thats the problem. I need help designing something that is portable, can be carried by a smaller person (I'm 5'6" and 115 lbs), will last a fair amount of time, and would make it ~350-400. At all the fields I play at, the outdoor FPS limit is 400 (at larger events MGs have a 350 FPS limit), so I want to build a design based around that.
For portability, I see that alot of people use Co2 tanks for a carryable platform. My budget is VERY limited, so I can't afford a Co2 regulator, tank, and constant refills, so that brings me to my next point: Could I just use compressed air from a tank? I just put the finishing touches on a back mounted large capacity tank for use as a versatile platform for a... Cough cough... water gun... cough cough, a dart gun, low power spudgun, and it is threaded with 1/8" threads with a reducer to go to a 1/4" hose to go to the platform that I decide to put on there. Could I use a blowgun attached to the hose, then going to the vortex block?
Thank you for your time, sorry if that is drawn out or hard to understand.

hmm if you are going to use an airtank, to keep it firing long time you need to use high pressures and a regulator, or you need to carry HUUGE airtank

What about a propane tank, you can use 1 full tank to supply the propane and an empty one for an expansion chamber, this should be cheap enough as propane tanks are only 3 bucks.

Welcome to spudfiles

With a 2 litre air supply on this project I got 4 seconds firing time from a 110 psi fill.

If you can't afford the CO₂ option, a large capacity low pressure backpack could be an option, but I would suggest you make it a point to have a BBMG that is as efficient as possible (some tips) - that way for example, you could get the performance you want from say 75psi, but have your backpack at 150 psi and with regged down feed that will make it last much longer.

try to find yourself a fridge compressor and a suitable tank (say an old air fire hydrant) so that you can pump it to 400 psi and have a fair capacity, with the economy modifications shown above by JSR.

Well, thanks for the advice.
I will probably try to do the 150 psi rig reduced down to 75 psi
Is it possible/safe to put compressed air into a large Co2 tank?

Its been done, just thread it on, a fire extinguisher would be a cheaper alternitive though, theres several threads about using them as tanks. Check gun freaks inline to see one used.