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What material should I use? PVC, Steel, or Copper. I need a cheap and easy to use material, that can hold up to 300 psi, and also I need it to be able to have grooves for O-rings to make a seal. Any ideas?

PVC. It can handle the pressure as a barrel and will be easy to put grooves in.

What sizes are you thinking of? Undamaged 1" (I think) PVC fails at about 1,000psi, so 300 would be safe at smaller diameters.

Ok. For a regular rifle stock, how big should I get the pvc? I need it to be able to shoot paintballs for sure. I will be getting a QEV from ebay some time, this weekend (if not ebay, I will make it on sunday.).

Well you can obviously discard PVC as it's pressure rating doesn't extend to such pressures. Unless of course the parts won't be exposed to any pressure, housing etc.

Steel often has a seam, it can be ground down but that can take some time. It's also a bit harder to work with compared to other materials.

Therefore I'd strongly recommend copper or aluminium. Copper isn't usually that cheap, aluminium is a little cheaper.

Aluminium has been used above 1000PSI in a hybrid, it's soft and easy to work and generally comes with a near perfect finish internally.

Copper can be soldered and is somewhat softer, though I wouldn't use it above 300PSI.

Brass can also be considered, it's a bit harder than copper, a little more expensive and can be soldered to.

I think I've ranted enough.

[Edit] If "perfect" PVC fails at 1,000PSI, why aren't we using it in high pressure pneumatics?

As a barrel PVC would be fine, until you get a jam of course.

And if my memory doesn't fail me, 3/4 CPVC (conduit) fits paintballs well. Look in the Ammo discussion board, projectiles and barrel sizes are in a sticked thread.

I would possibly be working with 1 inch, but it will probably be interchangeable barrel sizes, so yeah.... Zeus, I think I will stick with pvc, since this is my first time, once I start getting good at this (and getting money for it..) I might experiment with others...

Seamless steel can be bought. If aluminium is available, I'd suggest that because of the density.

We don't use PVC because everyone bangs their guns around and drops them. We also like safety factors. A safety factor of 2x is pushing it.

Ok, well I am not sure.... I will most likely stick with pvc just for a first time, maybe copper, what ever can fit the QEV/Sprinkler valve...

You can make anything fir the sprinkler valve, all npt threads are the same... you just need a male adapter to attach to your barrel and it will thread right into your valve. I think you have a lot more research to do before you go building this.

Yeah, thats my idea.... I have it all planned out, seeing as my valveless works the same way. It has screw on barrels, so I can add up to 1 1/2" barrels (thats the size of the chamber, dont want to go bigger than the chamber for obvious reasons...).

ummmmm , excuse me if im wrong but isnt the bolt action after your firing valve so that means it just needs to be air tight but not supper tight as if you were going to pressurise it ? because all the air will need to do it just travel through the bolt and push the projectile out of the barrel?

No your not wrong I dont think. But I want to make sure I get the most out of it is all...

Bolt action can be done without o-rings by epoxying a thick rubber gasket to the back of the barrel, and having the barrel itself move within the bolt-action frame backwards, exactly like on Ragnarok's HEAL. The gasket could also double as a detent to keep looser ammo from sliding or rolling down the barrel, and also give some security to the bolt when it is closed (closing compresses the gasket, so that your bolt pushes against the frame when closed, keeping it from falling or being bumped open).

EDIT: Could have sworn it was HEAL, but I was wrong, HEAL doesn't use a gasket attached to the back of the barrel.

Rather, check out this cannon by SubsonicSpud.

Ok, Thanks mark. I am going to be getting some cash tonight so I will head out to lowes tomorrow, then after then I will try and upload pictures to show you guys what I have.

I am getting my dad to take me to a couple local firearm shops as I type. I will get pricing on rifle stocks and stuff and let you guys know how big the rifle will be, then start fully planning the gun!