SpudFiles

Hello again spud files I have a bit of a challenge for you. I built a beauty of a mortar this week in an attempt to build something to give my team an edge in airsoft games, it is powered by 12 gram co2 cartridges and a convergent-divergent nozzle to boost power. I went out to fire it today and sadly it only shot about 100 feet. I was wondering what might be wrong and if you guys could help, so here are the facts:
-it was about 30 degrees outside when i shot it, could this drastically effect the range?
-the barrel is 4 feet long with a two inch bore, but the air chamber is only eight inches long with a 1/2'' inside diameter. This seems like it is far from an ideal ratio.
-i was shooting a tennis ball and the air seal was not perfect.
One big question I have is if i need to ditch the 12 gram co2 system in favor of something better, if so what system might be better for increased range. I hope this is enough info for you guys and I hope you can help.

Temperature affects co2 a lot. Maybe the cartridge ran out of co2. What type of valve are you using? Got any photos?

just using a ball valve to vent the chamber, nothing fancy. I have one picture, but its terrible. Also I am using an entire cartridge per shot so the is not an issue with it running low on co2. Thank you very much for your help

Be careful using PVC with co2. The ball valve is probably limiting it too. Have you considered using a piston valve? Your gun will be much more powerful.

All of my pressure fittings are steel, I know better than to use pvc for those parts. thanks for the advice with the piston valve, i will look into it.

madmarcs wrote:-it was about 30 degrees outside when i shot it, could this drastically effect the range?

Yes - carbon dioxide pressure is very much affected by temperature.

-the barrel is 4 feet long with a two inch bore, but the air chamber is only eight inches long with a 1/2'' inside diameter. This seems like it is far from an ideal ratio.

Not too much of an issue if you're using higher pressures.

-i was shooting a tennis ball and the air seal was not perfect.

Doesn't help.

One big question I have is if i need to ditch the 12 gram co2 system in favor of something better, if so what system might be better for increased range. I hope this is enough info for you guys and I hope you can help.

Your ball valve certainly isn't helping, I would recommend switching to a solenoid valve. If you want to use this in cold weather, compressed air is a better idea.

Thank you guys very much for your help with this problem. I took your advice with the valve and switched it out for a modified sprinkler valve and waited for a warmer day. I took it out and shot it when it was sixty degrees Fahrenheit outside and i noticed minimal difference. my other problem is no matter how much Teflon tape and binary epoxy i use the valve wont seal properly and i still don't get any real distance with this thing at all. Any more ideas to help me fix this problem?

madmarcs wrote:Any more ideas to help me fix this problem?

How loose is the projectile in the barrel? Without a reasonably tight fit performance will always suffer.

Regarding the leaks, could you take some closeup pictures of the problem area?

I wrapped the tennis ball with electrical tape and if fits snugly now so that is not an issue. as for the problem areas on the valve i have some pictures, but they are terrible. I seem to have always been cursed with pressure leaks no matter what I try to fix them with. Im thinking about just running compressed air through this system with a bigger chamber so that i don't have to worry about the co2, but then i would have to pressurize it with a bike pump in the field, which would just take too long. This cannon has turned into a real problem child.

i did another pressure test today and every single seal on my sprinkler valve leaked. I have sanded everything and filled every hole with 2 part epoxy and this thing WILL NOT WORK. I am done wrestling with this thing and i need something that will work. what kind of valve could i make or buy that would work instead? i have a 1/2 QEV valve but i don't know if it could handle the pressure.

http://www.spudfiles.com/pneumatic-cann ... c7133.html

There's no way your 8" by 1/2" chamber is big enough. If you roughly calculate, depending on ambient temperature, blah, blah, you are trying to put over 2000psi on your sprinkler valve, which is designed to hold 80 - 150 psi. No wonder it leaks. Just get a bigger chamber and the 12 gram system should be fine. And put a gauge on it. They aren't expensive and that will solve a lot of your performance mysteries.