Cellular Core ABS Cannon

[CalvinB]

I have been planning to make a cannon to launch Nerf Mini Vortex footballs. The idea is to make a man portable "rocket launcher" for airsoft that is 4" diameter by 40" long using a 2" barrel inside of the 4" chamber and a pilot valve (I have been researching this quite a bit). As you all probably know 4" PVC and fittings are $$$ compared to cell core ABS. So I started to research it as a possible option and here is why:

Cost
Shock resistance vs. PVC
Failure Mode vs. PVC
Weight (I already carry 45+lbs of crap)
I only need to shoot a small foam football about 150-200 feet (the community doesn't want these things too high powered as we shoot them at other people)

So my question is, what kind of pressure would it take to get a Mini vortex that far with a 1.7/1 tank to barrel ratio, and is that well within the "unrated" pressures that cell core ABS can take?

Before any flaming, I know there is a search, I used it, I found one thread where someone has actually tested the strength of ABS. I am mostly looking for people that have used and tested this material themselves, I don't care if a friend of a friend had one fail, I want to know what you have seen/ built first hand.

Thank you all in advance.

[jackssmirkingrevenge]

Some quick modelling in GGDT shows that with such a large chamber volume and fast valve, you're really not going to need much pressure for reasonable velocity.

Do you intend to lob this at a high angle trajectory though, or fire it directly? That would significant affect the required velocity for your range target.

How much does the mini-vortex weigh?

[Technician1002]

I think you found my thread..

I found one thread where someone has actually tested the strength of ABS.

I'm still here if you have any questions on the cannon. The cannon is in my sig below.

I have not tested it to destruction, but I have a feeling the stuff will hold higher pressure than a 2 liter pop bottle.

Be sure to seal all cut edges of the pipe exposed to chamber pressure. I found some of the core by some manufactures will bleed air through the core. I had to seal the edges of my 2 inch pipe ports to prevent air from getting in the core under pressure.

At higher the launch forces will tear the tail off the mini vortex. To keep it in one piece, you will want lower pressure.

I do know that at 60 PSI and up, my eyesight is not good enough to see where a golf ball lands when tested for distance. It is over 350 yards.

[CalvinB]

Angle doesn't matter a ton, it rather lob it than blow on the gun. I was thinking about 30 degrees max though, for realism/accuracy sake.

the only weight I can find is 8oz which is .226 Kg for the kinematics

[CalvinB]

I think you found my thread..

Be sure to seal all cut edges of the pipe exposed to chamber pressure. I found some of the core by some manufactures will bleed air through the core. I had to seal the edges of my 2 inch pipe ports to prevent air from getting in the core under pressure.

It was your thread actually, I recognize your profile pic. What is the best way to seal the edges? I am a novice with PVC and an ABS virgin so I am a lit hesitant. I know that you built yours to fail but what would the best way to help prevent failure.

One more for now, how do you think it would do with a shock at about 40 psi?

[Technician1002]

I simply used a long handle hemostat to hold a cotton swab to paint the exposed edge with ABS cement. It would have been much easier to do before it was glued together. The leak through the core was noted bubbling out the breech before I added the cap. I was doing an initial pressure test.

The air leaked from inside the chamber, through the barrel core and leaked out of the core at the breech. I thought it was an the ring leaking when I first heard it, but the soap bubble test revealed the exit point. Before I found the leak, it had me baffled. After the pressure was added, it began leaking. After the air was let out, it still continued to leak due to the pressure in the core. My fear was pressure in the core would de-laminate the pipe. It never did, but I sealed it just to be safe.

[Moonbogg]

I built a 4" chamber, 2" barrel advanced propane combustion cannon with cellcore ABS and it held together fine. The pressure was probably around 100PSI and it took probably a few hundred shots at least before I built a new cannon (not because it broke or anything, I wanted something more powerful). Anyway, all i'm saying is I would trust the stuff at lower pressures for sure. It is a proven material.

[dewey-1]

How much does the mini-vortex weigh?

The non whistling ones weigh 30 grams.

[jackssmirkingrevenge]

The non whistling ones weigh 55 grams.

With the launcher specifications, I would say 15-30 psi would suffice for good enough range and a flat enough trajectory to allow aiming.

If combusions are allowed you might want to consider using a single 2" tube as both barrel and chamber, with a 40" tube and the projectile placed say 25" away from the muzzle performance should be more than adequate.

[dewey-1]

The non whistling ones weigh 55 grams.

Sorry JSR but you are too fast for me.
I was editing the correct weight while you already quoted me on the first wrong weight.

[Technician1002]

Hmm, 30 or 55 grams.. The light one must be the one with the tail blown off.

[CalvinB]

What would be the best way to seal up the gun super tight, the idea is to charge it with a pump, carry it around charged, and use it one time in a 2 hour portion of a game. So ideally it would not lose a significant amount of air in that time

[Technician1002]

O rings on a piston work fine if made well. Leak test the launcher and seal all leaks and it should hold pressure for a very long time.
Mine leaks simply because I did not polish the o ring grooves after they were cut with a saw. The little metal version, the Marshmallow Cannon and the larger brother the 2 inch QDV (T shirt cannon) seal very well.

For safety, I fill them just prior to firing. I don't leave them with a charge in them.

The rate it drops in pressure is directly related to the rate it is leaking.