SpudFiles

soda stream bottles are alu as well, nowdays most hp tanks are alu because they don't rust. i doubt the threads on them will be anything you can get at the hardware store.

ah well. I was put off paintball tanks at first because they are quite expensive (filled) , but then I saw this brand new one for 10 quid , not bad.

http://cgi.ebay.co.uk/20oz-co2-paintbal ... 500wt_1156

trouble is i have no idea how i would fit it to my guns 15mm pipes. What adapters would i need?

You can buy an adapter that brings them to NPT threads here in America, so I bet there's a similar thing that can bring it to metrics where you are. Probably one on ebay... might as well buy it with the tank.

I've got one of these, the thread (called ASA or CGA320) is the same as a 1/2" BSP so you'll have no problem attaching to your 15mm pipe, buy a female 1/2" bsp adapter and seal with either an o-ring or epoxy.
you will also have to drill out the pin valve (gives you better flow as well)

something like this mate?

http://cgi.ebay.co.uk/5-x-Chrome-Female ... _500wt_922

yep, you might have to hack saw off the unthreaded tip of the tank valve, as the threaded bit is quite far down, I'll try and dig out a pictue of mine tomorrow.

I seen some discussions on the internet that suggest it is not safe to fill co2 bottles with air because

1.) it cant take that much pressure
2.) it would leak when used with air?

I think this is a load of rubbish but i just want to be given the all clear that I will be ok using that tank for my project. I only intend to pump it to 400 psi as it will be a portable system ( no compressors)

thanks

I would guess the discussion was whether it was safe to interchange CO2 and HPA painball tanks for paintballing, no it's not. At room temperature CO2 liquifies at about 900psi so this is the most pressure you will get in a CO2 tank and what the tank will be rated to hold (a bit higher for if the tank is heated up). HPA (high pressure air) tanks are filled to several thousand PSI so need a much higher pressure rating.
However As you're only going to 400 psi a CO2 tank should be fine.

well if its a co2 tank it can take at very lest 2k psi, the only problem is if its a steel tank it could rust. use epoxy or loctite to seal the threads and you'll be fine

I would like some formulas to work out how large my secondary chamber can be to get 5 shots before the pressure in the primary chamber drops from 400 psi to 300psi. ( 20 psi per shot basically).

my primary chamber is a 20oz paintball tank which stores the air. The ball valve is then opened to fill the secondary chamber which is used to fire the pellet.

Here you go
http://www.1728.com/boyle.htm

*Update*

have installed 6mm steel barrel
paint ball tank fitted

Il upload pictures after I have got the couplings to add the secondary firing chamber.

Sorry for the double post but would this kind of setup be suitable for a multi-shot?

http://s785.photobucket.com/albums/yy14 ... tled-3.png

thanks

you can use a 3way valve inplace of the 2 ball valves, but yea it will be semi.

Yep that will work, a three way valve will make it more compact and better looking, also easier to operate and give you semi auto, but the ball valve method is a simple way to do it too.