SpudFiles

Hey guys, I'm planning on making an air pressure cannon that shoots the led balls out of shotgun shells. I'm going to get a normal sized barrel that screws strait into the ball valve and put a piece of dowel the right size into the barrel. I am going to get some really small metal pipe from the hobby shop that will fit the led ball very nicely. The rest of the gun will be just like a marble shooter. and i hope to pump it up to about 120 psi. Do you think this will work? Post a comment if you think it will work or it wont work at all.

Cheers, Tom

So your trying to build a cloud? A drawing or diagram of some sort would be helpfull.

Welcome to Spudfiles.

Your idea will increase the energy transfer since the working area of the barrel is much larger than the ammo's diameter but it has a couple significant problems. The most important is how do you stop the stick?

I would suggest just using the correct sized barrel for the ammo. If you want better performance then get a better valve, ball valves significantly limit performance, they take too long to open.

Or, drop the stick and go with an oversized barrel and sabot the ammo.

My 2.5mm calibre pen-gun has really poor performance with lead shot and that's at over 300 psi, a single shot rifle type launcher won't be worth it. A cloud BBMG on the other hand, that would be a different story

soo jimmy101 what sort of valve do you suggest ? and i would have the right sized barrel for the ammo because i would drill a hole through the dowel and the small pipe the right size for the ammo would go in.
and whats the stick?

Don't bother using spherical ammo for such a small bore. They can in fact give quite good performance but only with long projectiles. Something like a ball point cartridge which is about 2.5mm thick is perfect.

ok so round ammo would not work very good. so i am back to making just a marble shooter. thanks anyway guys.

Do you think i should give it hop up?

Draw a diagram. Cuz its kinda confusing. Anyway, shotgun shells usually use Sabots which are a kind of "container"for all the bullets. The sabot fits the barrel perfectly, and then the smaller ammo goes inside the sabot.

EDIT: Oh yeah, and EDIT your posts instead of doing 2 posts in a row. (see im editieign it =DD) Its just that some people get annoyed for some reason. I guess its because it wastes space but theres no problem for me...

For a small bore I would just go with either a sprinkler valve or a dishwasher / clothes washer water control valve.

from here

A small piston valve would be even better but it'll be more work.

The "stick" was the "dowel" you referred to in your first post. I assumed that you were using it as a sabot to transfer the force from the large tube into the smaller barrel.

I believe he intends to use the dowel (or at least a piece of it) to fabricate a reducer bushing.

Round ammo will work fine. Marbles were still round when I last checked.

The problem is one of bore size and low pressure.

Remember that the area you give the pressure to act upon (bore size) will be a factor in determining how much force is available for acceleration of your projectile, and along with such things as barrel length, and projectile mass, will have an effect on its velocity.

By using a comparatively low pressure (120psi) along with a small diameter bore, you are compounding the effect.

The result will be fairly unimpressive regardless of valve type.

Build the marble shooter, you'll be happier.

jimmy101 wrote:For a small bore I would just go with either a sprinkler valve or a dishwasher / clothes washer water control valve.

For such a tiny bore it would be easier to go with a blowgun directly, and unless you're using ridiculously high pressure it's hardly worth making it single shot either.

I always wanted to make a 2-3mm calibre BBMG, the only thing that stopped my so far is finding a reliable supply of lead shot.

Talking of tiny calibres, Interesting note for UK spudders limited by 12 ft/lb regulations and with plentiful supplies of high pressure helium: an 0.130" diameter N^o. 4 lead ball at about one fifth of a gram travelling at the speed of sound is still technically legal

Haha. I'm back to making a marble shooter now. Would 120 psi be good for a marble? or should i make it so it can handle a higher pressure? Would this gun pass Australian regulations without having to have a gun license? Has any one else made a marble gun like mine? With the ball valve and things?

120psi would be adequate for a marble shooter with a modified sprinkler valve.

If you have the capabilities to make a piston valve, (or if you can buy a qev) then by all means, build it to take higher pressures.

I doubt very much it will be even remotely legal in the land of Aus.

Check the pneumatic canon showcase. Many ideas to choose from, and yes, even some with ball valves.

Yeah 120 PSI is really really high for Australia. I live in australia and my shots are like, 50psi.
Usually UK standards are the same for Australia. So what jackssmirkingrevenge said was that you cant have more than 12ft/lb or something. (wtf is 12ft/lb)