Modeling a gun

[Modderxtrordanare]

I'm planning on building a gun that shoots pingpong balls really fast. But I have a few questions.

First, did I model the gun right to be using unregulated CO2 (or is it more than 800psi unregulated) in a 2" chamber? Also, did I model the 1" burst disk right?



It gives me the error that my barrel is too long, but when I make it shorter it warns me of gas liquification. What do I do?


Last question, (for now) what size barrel fits pingpong balls decently with little or no wadding?

[Velocity]

I think the pressure in a full CO2 cylinder is closer to 850 PSI at 70 degrees

1.5" SCH 40 PVC pipe fits ping pong balls great... though, you might want to look into a metal barrel to stand the blast of CO2.

Are you sure you have the weight of a ping pong ball correct? I find it surprising that a ping pong ball weighs less than a paintball... though I suppose it could be true.

I am not sure whether the ping pong ball would be destroyed from the shock of the CO2 blast.

As I am sure you already know, make sure to have all components before the barrel rated well above 1000 PSI, and be sure that they can take the cold temperature of the CO2. If I were you, I'd make sure the barrel was rated above 1000 PSI as well... just as a precaution.

[Modderxtrordanare]

The union is rated to 3k psi. But I don't know what the pipe is rated to.


Pingpong balls most definetly weigh less than a golf ball, they're a thin, hollow, plastic shell. Pingpong Ball Regulations.

[Orpackrat]

Before the barrel, steel pipe and ball valves from a hardware store can handle the pressure just fine. I recommend putting a dozen drops of pneumatic oil every other time you put on a Co2 tank (9oz and above) to keep the valve in good working condition. I have built several cannons using SCH 40 PVC pipe for the barrel without any problems. Once the cannon fires, if you have a short barrel, the gas won't turn into a liquid just because your barrel is shorter.

I believe (have not tried though) that a ping pong ball will survive the rapid acceration from un-regulated Co2. A ping pong ball should easily be much lighter than a paintball. Due to how light a ping pong ball is, it should have no problem reaching high speeds but I also don't think its going to get good range.

Just curious, are you going to use a duel valve setup? One fills an expansion chamber, is closed, and the other releases the gas from the expansion chamber without loosing excess Co2 from the tank.

[Modderxtrordanare]

Before the barrel, steel pipe and ball valves from a hardware store can handle the pressure just fine. I recommend putting a dozen drops of pneumatic oil every other time you put on a Co2 tank (9oz and above) to keep the valve in good working condition. I have built several cannons using SCH 40 PVC pipe for the barrel without any problems. Once the cannon fires, if you have a short barrel, the gas won't turn into a liquid just because your barrel is shorter.

I believe (have not tried though) that a ping pong ball will survive the rapid acceration from un-regulated Co2. A ping pong ball should easily be much lighter than a paintball. Due to how light a ping pong ball is, it should have no problem reaching high speeds but I also don't think its going to get good range.

Just curious, are you going to use a duel valve setup? One fills an expansion chamber, is closed, and the other releases the gas from the expansion chamber without loosing excess Co2 from the tank.

I'm going to use a burst disk.

[spudthug]

how are you going to keep liquid c02 out?

when you shoot the ping pong ball it may dent in but thats about it...it obviously shouldnt shred.

why are u getting unthreaded pipe? r u welding it?

good luck on this!!!!!


btw check out my new hybrid guys!!

[Modderxtrordanare]

how are you going to keep liquid c02 out?

when you shoot the ping pong ball it may dent in but thats about it...it obviously shouldnt shred.

why are u getting unthreaded pipe? r u welding it?

good luck on this!!!!!


btw check out my new hybrid guys!!

Does it really matter if I have liquid CO2 in there or not? I'm not using a valve that can get destroyed by it, I'm just using a burst disk.

Yes, I'm welding it.

What kind of material would I use for a burst disk at that high of a pressure?

[joannaardway]

I can promise you that you will not get 2000 ft/sec - utterly impossible.

Not that the problem is your mistake. GGDT demonstrates some modelling flaws at particularly high velocities.

Sure, you'll get a fair bit of power, but the velocity will not be beating 1000 fps - it would be nigh on impossible to do with CO2.

[Orpackrat]

Does it really matter if I have liquid CO2 in there or not? I'm not using a valve that can get destroyed by it, I'm just using a burst disk.

What kind of Co2 source are you going to use? Expanding Liquid Co2 will cause you cannon to ice over, the lower temperature will lower the pressure of the Co2.

If I understand correctly you cannon is basically Co2, burst disk, barrel, like #3. If building like that I would recommend using 12 gram Co2 disposable cylinders. You would only get one shot per Co2 cylinder but they would be more consistant shots with very minimal Co2 wasted.

If using a constant Co2 source (refillable tanks) I would recomend putting a valve in to turn the tank on and off, like in #2. This way you can turn the ball valve on and once the cannon fires close the valve to prevent wasting Co2 out the barrel (would get very expensive wasting Co2 out the barrel).

I prefer to use a duel valve system to be efficient and consistant like in #1. The first valve simply turns the tank on and off to fill the expansion chamber. Once expansion chamber is filled and fill valve is closed the Co2 has time to expand and warm up for maximum pressure. The second valve is opened allowing the cannon to then fire with the burst disk. It only uses the gas from the expansion chamber and none is wasted from the tank. Close second valve, install new burst disk, and repeat cycle.

[Modderxtrordanare]

I can promise you that you will not get 2000 ft/sec - utterly impossible.

Not that the problem is your mistake. GGDT demonstrates some modelling flaws at particularly high velocities.

Sure, you'll get a fair bit of power, but the velocity will not be beating 1000 fps - it would be nigh on impossible to do with CO2.

1000 fps is no where near impossible, it's been done lots of times. Even joel did it.



Then again, you don't have to go much past 1000fps to break the sound barrier. Only 1115fps (760mph)

[Velocity]

Joel used helium in his cannon... COMPLETELY different from using CO2. Helium gas is lighter than air, while CO2 gas is heavier than air.

EDIT: Random tangent, but I found it kind of surprising that you said "even Joel did it"... its funny considering that Joel's life was devoted to spudguns for years; he owned the most respected spudgun site and store. Yet you sound suprised when you say Joel broke the sound barrier... I would EXPECT him to do it out of anyone.

[chartreusesnot]

How do you know Joel used helium? I've seen only a few references to that gun, and it mentions nothing of helium... and, is helium better than atmospheric or CO2?

[jimmy101]

Helium is often used in guns for supersonic shots because the speed of sound in helium is considerably faster than in air, CO2, N2 etc.

To get the projectile going supersonic the gas behind the projectile has to be super sonic... well sort of. Since getting the gas in the gun going supersonic is usually a BIG problem, the solution is to use a gas that has a much higher speed of sound in the gun. Now you can get the gas going say Mach 0.9 in the gun but that corresponds to greater then Mach 1 in the air outside the gun.

Another approach is to use hot gas in the gun. The speed of sound goes up as the temperature of the gases increases. (In a combustion gun, the speed of sound in the chamber is in the 2000~3000 FPS domain at the peak pressure and temperature.)


Back to the OP, why try to get a ping-pong ball going so fast? With the tiny sectional density (mass / area) of a ping-pong ball it is going to slow down very fast. If you do hit Mach 1 it'll be going Mach 0.5 by the time it has travelled 20 or so feet.

[joannaardway]

1000 fps is no where near impossible, it's been done lots of times. Even joel did it.

Then again, you don't have to go much past 1000fps to break the sound barrier. Only 1115fps (760mph)

As other people have told you, helium is fine for going supersonic.
CO2 is not. The gas is very dense (relatively), which gives it a particularly low speed of sound.

Other than severely heating the CO2 to insanely high temperatures, then don't expect to go supersonic with it.

Pressure has very little to do with the maximum attainable speed.
To give you an example, to get to 1200 fps with CO2 at about 70F, then you'd first need a molecularly perfect barrel - completely frictionless to avoid sonic shockwaves. And even then you'd need over 5000 psi (at that point, not initial pressure) - which you can't get at 70F.

I can promise you that CO2 is certainly not what you want for supersonic rounds.
It's fine for putting out heavy rounds at reasonable speeds - which gives you lots of energy, but getting anything going much over 800 fps is going to be a real struggle with it.

(The earlier mention of 1000 fps was a note that few cannons using regular compressed air [much lighter and with a higher speed of sound] can beat that.)

And you do have to go a lot past 800 fps (a optimistic maximum anyway) to get to 1115 fps. And 2000 fps is certainly completely impossible. (CO2 molecules simply can't travel that fast)

Either switch your gas to something lighter (to allow higher muzzle velocities), or switch your ammo to something heavier (to allow higher muzzle energies).

I'm not arguing with you because I have something against you or because I don't think you deserve to go supersonic.
I'm telling you that it really is impossible to do it this way, and trying to is going to be - at best - a waste of your money.

[Modderxtrordanare]

1000 fps is no where near impossible, it's been done lots of times. Even joel did it.

Then again, you don't have to go much past 1000fps to break the sound barrier. Only 1115fps (760mph)

As other people have told you, helium is fine for going supersonic.
CO2 is not. The gas is very dense (relatively), which gives it a particularly low speed of sound.

Other than severely heating the CO2 to insanely high temperatures, then don't expect to go supersonic with it.

Pressure has very little to do with the maximum attainable speed.
To give you an example, to get to 1200 fps with CO2 at about 70F, then you'd first need a molecularly perfect barrel - completely frictionless to avoid sonic shockwaves. And even then you'd need over 5000 psi (at that point, not initial pressure) - which you can't get at 70F.

I can promise you that CO2 is certainly not what you want for supersonic rounds.
It's fine for putting out heavy rounds at reasonable speeds - which gives you lots of energy, but getting anything going much over 800 fps is going to be a real struggle with it.

(The earlier mention of 1000 fps was a note that few cannons using regular compressed air [much lighter and with a higher speed of sound] can beat that.)

And you do have to go a lot past 800 fps (a optimistic maximum anyway) to get to 1115 fps. And 2000 fps is certainly completely impossible. (CO2 molecules simply can't travel that fast)

Either switch your gas to something lighter (to allow higher muzzle velocities), or switch your ammo to something heavier (to allow higher muzzle energies).

I'm not arguing with you because I have something against you or because I don't think you deserve to go supersonic.
I'm telling you that it really is impossible to do it this way, and trying to is going to be - at best - a waste of your money.

I in no way think that you would have something against me or anything of the sort. Your posts, among a select few others are the most informative posts I see on this forum.

I assume just hit up a SCUBA shop or a welding supply company of sorts for the helium? Is there a need for a special sort of regulator, or would one used for CO2/N2 work?