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Normal FPS for a simple pneumatic

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Normal FPS for a simple pneumatic

Unread postAuthor: sharpshooter11000 » Fri Aug 26, 2011 6:14 am

Could anyone tell me what the normal FPS for a simple pneumatic spud gun is at 100PSI? mines firing at about 150 FPS with a cork, is this low or normal? (sorry if this is in the wrong section, I'm new here)
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Re: Normal FPS for a simple pneumatic

Unread postAuthor: jackssmirkingrevenge » Fri Aug 26, 2011 6:28 am

*sigh* after the whole bad example thread debacle... I'll go easy as it's your first post.

sharpshooter11000 wrote:normal FPS for a simple pneumatic spud gun is at 100PSI?


You need to provide a lot more data for a relevant answer, at least the following:

-barrel length
-chamber volume
-projectile weight
-valve type

How did you measure muzzle velocity?
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Unread postAuthor: sharpshooter11000 » Fri Aug 26, 2011 6:36 am

Sorry looking back I very unspecific. The barrel length is 2ft of 22mm copper pipe, the valve is a ball valve, the chamber is one of the small oxygen tanks and the ammo was a cork from a wine bottle (about 5-6g). I measured it with the sound recording method and put it on audacity.
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Unread postAuthor: jackssmirkingrevenge » Fri Aug 26, 2011 6:49 am

How are you opening the ball valve?

For good performance with such a light projectile it needs to open fast, in the sense you'd have to knock it open with the edge of your hand as opposed to gripping it the normal way. Consider spring loading.
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Unread postAuthor: sharpshooter11000 » Fri Aug 26, 2011 6:59 am

Yeah I've considered it but I only made the gun yesterday so haven't got round to it, at the minute I'm just flicking it open with the palm of my hand.
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Unread postAuthor: jackssmirkingrevenge » Fri Aug 26, 2011 7:06 am

In short, that's about the performance I'd expect given the parameters you gave.

Also, remember that a cork has a very poor density, so it slows down quickly in air - and as the audacity method gives you the average velocity between muzzle and target, it's bound to be on the low side.

You're using relatively low pressure, light projectile and short barrel, so the ball valve isn't doing you any favours.

Rather than piss around with spring loading, I would recommend getting one of these.
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Unread postAuthor: sharpshooter11000 » Fri Aug 26, 2011 7:15 am

All of the gun is made with copper pipe and compression fittings and the tank can hold 2,800PSI, how many PSI do you think it could hold? Also I can put on a longer barrel, would you reccommend that? I looked at a QEV, does it make a right angle though? And how do you trigger a QEV?
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Unread postAuthor: saefroch » Fri Aug 26, 2011 7:22 am

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Unread postAuthor: sharpshooter11000 » Fri Aug 26, 2011 7:26 am

Thanks but as you can see I'm new to all this so how do I pilot it and which opening do I put my air tank on to?
Edit: oh right I get it now but I think I'll just stick with a ball valve for now. Would having a longer barrel make any difference?
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Unread postAuthor: jackssmirkingrevenge » Fri Aug 26, 2011 7:36 am

What saefroch meant was "There's plenty of information on the wiki and posted in the forum, why don't you search a little and if that still doesn't answer your questions, you can ask again here."
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Unread postAuthor: sharpshooter11000 » Fri Aug 26, 2011 7:42 am

I have looked at the wiki and other posts, that's why I get it now. I'm asking about a bigger barrel and PSI because I can't find many people who build with 22mm copper and compression fittings :(
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Unread postAuthor: jackssmirkingrevenge » Fri Aug 26, 2011 7:46 am

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Unread postAuthor: Crna Legija » Fri Aug 26, 2011 7:50 am

I don't know how much volume there is in ''one of the small oxygen tanks'' but if its more than your barrel, then evening them out will be good.

If you are sure all the compression fittings are tightened all they way down then it will be safe to 300psi.
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Unread postAuthor: sharpshooter11000 » Fri Aug 26, 2011 7:53 am

I've seen most of them but they don't answer my questions. I'm guessing that a longer barrel will help and that I can get it up to 200 psi without anything breaking?
Thanks for your patience, I'm not the best at the whole spud gun thing... Or the forum thing for that matter :oops:

And yes the "small oxygen tanks" have a lot more volume than the barrel
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Unread postAuthor: jackssmirkingrevenge » Fri Aug 26, 2011 7:57 am

sharpshooter11000 wrote:Thanks for your patience, I'm not the best at the whole spud gun thing... Or the forum thing for that matter :oops:


People usually start off with the wrong questions, so I will ask you a few of my own:

- what performance are you after?

- what materials, tools and experience do you have?

- does the size of the launcher matter?

- does the noise made by the launcher matter?

- how much are you willing to spend?

- what are you using to pressurise the chamber?

- What is the airspeed velocity of an unladen swallow?
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