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QDV ammo

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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QDV ammo

Unread postAuthor: LeMaudit » Fri Feb 05, 2010 3:00 pm

Hi Guys,

Following JSR footsteps, I am seeking the Holy Grail for compactness! ;-)

I am still struggling to find time to reinstall my machinist workshop, and in the meantime I read and learn from the forums and the web. Yeah, I know I said the very same a long time ago (for those who have a very good memory)… too much real work; what can I do?

Here’s my most recent concept drawing: a kind of miniature QDV, with integrated Schrader valve inside the piston. I would like very much to have your opinion on it as I really want to build this one in a month or so.
JSR, maybe you already tried that years ago? Now I would not be surprised! ;-) I did some extensive search on the forums, and looked with great interest the experiences using this QDV on large calibers, but couldn’t find something quite like mine.
Any suggestions/ideas about performance or how to improve it?

My goal with this design was:

- Compact, for maximum power in minimum space. This current design roughly to scale is 4” long, dia. 1”. Which is a rather large but manageable ammo.
- No dead volume, because it’s a so small chamber.
- Design usable for breach loading, to be able to load easily darts or other objects or even change the barrel caliber easily with the same chamber.
- Can become a separate cartridge for quick reloading. Can you imagine the large double barrel shotgun out of those baby nukes? I can :-D
- Safe (call me chicken) for storage or handling while loaded
- Air flow not restricted (as much as possible) by some internal part.
- No complicated parts, just 2 floating O-rings and a tapped hole for a Schrader valve to build the piston.


About safety, here’s what I had in mind:

- A leak on the Schrader would not fire the projectile as in a pilot valve.
- A leak on the O-rings would keep the same pressure balanced both sides until there’s no pressure left, so no accidental discharge either.
- A positive secured lock is easy to achieve under pressure at the back of the ammo because the forces involved are balanced inside the chamber.


GGDT gives me some interesting figures using this 9/16” ammo: @ 400psi, almost 50 ft*lb for a 20” long barrel. I like it. But maybe GGDT is a bit optimistic… is it?
I choose a burst disk as I don’t know of to define a QDV with it. I bet a QDV is really fast as my understanding is that the pressure will push open the piston as soon as it start opening; hence the rubber washer to cushion the shock on the piston.

Another idea: What I really have in mind, is not to let the Schrader go to the right as in the diagram when fired, but fix the schrader to the gun body and let the whole ammo go to the left, and in the same time engage in the barrel to avoid pressure leakage during firing. But that’s another story and I’ll develop it if you have questions.
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Attachments
gun7.png
QVD ammo. Sketch to scale. 4" length, 1" diameter, 9/16" ball bearing.
gun7_GGDT.png
GGDT simulation @ 400psi for a 20" length barrel. Overall length including ammo ~ 24"
gun7_GGDT.png (15.72 KiB) Viewed 1596 times
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Unread postAuthor: ramses » Fri Feb 05, 2010 3:49 pm

Interesting idea. It reminds me of Clide's HEAR valve that he used on the GB semi. It worked very well in that application.
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Unread postAuthor: Demon » Fri Feb 05, 2010 4:01 pm

Are floating o-rings essential for a perfect seal on moving parts? When the piston goes forward or backward, should'nt the floating space make a leak for a small amount of time ?

And if you want compactness, try PCP and 6mm bb's
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Unread postAuthor: LeMaudit » Fri Feb 05, 2010 6:35 pm

Floating o-rings are just a very easy way to have a seal without close machining tolerance. Some sites explain it very well, here's one (this link was already given here... was it by Gippeto?)
http://www.rlhudson.com/O-Ring%20Book/d ... namic.html

Hmmm... it could be that there's a small leak when the piston move backward, but I think it will make no difference because it happens so fast. This design is not new anyway. As an additional deature, as soon as the piston is fully backward, it seals itself on the rubber washer.

As for PCP and 6mm bb, I'm afraid it would be against Canadian laws because the speed would be too fast for a decent muzzle energy.
I think my design would be brute force, heavy projectile and under the 500 ft/s limit so absolutely legal for Canadians :-D (was design with that in mind to be honest ;-) )
GGDT gives me for the same barrel/chamber using a 6mm steel BB "only" 12.4 ft/lb, but a 642 ft/s which is illegal here.
To stay legal and below 500 ft/s I would have to reduce the pressure to 200psi, which would provide a ridiculous 7.3 ft*lb. The same of a very ordinary BB rifle in fact.

(if I'm wrong, please tell me so...)
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Unread postAuthor: Gippeto » Fri Feb 05, 2010 7:47 pm

Okay....to clarify things a bit...

Velocities over 500fps are not illegal...airguns over 500fps are classed as firearms and can be registered and legally owned/used.

Even "home built" airguns can be registered.
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Unread postAuthor: LeMaudit » Fri Feb 05, 2010 9:00 pm

Sorry, my bad... English.
I meant illegal without a proper license... I should know I have one for my Diana airgun :-)
Hey, I didn't know home built could be registered Gippeto. Great then... I'll push the pressure up :-D
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Unread postAuthor: jackssmirkingrevenge » Sat Feb 06, 2010 1:36 am

Nice design :) though to be honest I don't see the advantage over a similar exhaust design with a spool piston.

Image
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Unread postAuthor: LeMaudit » Sat Feb 06, 2010 9:07 am

Thanks :-)

I considered this one, and a few others while digging the forums for ideas.

I'm afraid that a leak in the schrader would result in an accidental firing. And you have no way to positively "lock" the mechanism to prevent it. At least I couldn't imagine one without complicated contraptions :-D Mainly for me the reason to search a way to miniaturize a QDV which I feel very safe. Just a feeling though...

Of course if you fill the cartridge and fire immediately, it's not a problem.
But if you have a few ammo loaded and stored (or say, hanging in your belt or across your chest ;-) ) you surely don't want that to happen.

If I'm not mistaken, another little detail is there's a (small) dead volume with this design. And of course I suppose the full opening should take a bit longer with a pilot volume than a QDV.

So, I tried to improve all those little things. It surely is more complicated to build, but not that much I hope.
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Unread postAuthor: jackssmirkingrevenge » Sat Feb 06, 2010 9:21 am

I think if a schrader had to leak, it would do so at a tiny rate, not enough to fire the cartridge. still, nothing wrong with being careful ;)

How about this design, if you want to do some machining...

Image

Similar to the ideas you had expressed here ;)
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Unread postAuthor: spudtyrrant » Sat Feb 06, 2010 9:24 am

LeMaudit wrote: I'm afraid that a leak in the schrader would result in an accidental firing.
i for one have never ad a leak in a schrader (even at high pressure) i don't think this would be a problem if you decided to do this design instead
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Unread postAuthor: LeMaudit » Sat Feb 06, 2010 9:43 am

Good to know a schrader is not supposed to fail (or will do slowly) :-) Still, there's this positive locking I wish to have on preloaded cartridges. Any idea how to implement that with a spool valve (or similar design with a pilot volume)?

JRS: nice you remember my early contraptions :-D
I like this design! :idea: I discarded my early idea based on a quick coupling for a first try, to be able to fire various ammos and not only specific that fit the locking mechanism. But I'll keep it in mind. Using an existing coupling was manageable, but it is much more difficult to machine! :shock:

I can't wait to have my little machine shop operational again!
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Unread postAuthor: POLAND_SPUD » Sat Feb 06, 2010 9:54 am

I like it...

but do you know that you can design a partially balanced spool valve that would also load ammo ?
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Unread postAuthor: LeMaudit » Sat Feb 06, 2010 9:57 am

POLAND_SPUD, I'm not sure to understand but now I'm curious :-D
Do you have a link or a picture?
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Unread postAuthor: Demon » Sat Feb 06, 2010 10:37 am

To stay legal and below 500 ft/s I would have to reduce the pressure to 200psi, which would provide a ridiculous 7.3 ft*lb. The same of a very ordinary BB rifle in fact.

(if I'm wrong, please tell me so...)


To be illegal (as i am canadian) it needs to be 500 fps AND over 4.2 ftlb

My current project is an onboard airtank 3 way valve bullup semi-auto (kinda a long name) and from what i calculated, i can shoot 8 .43 gram bb's at 500 fps with one refill (one refill is 8 bike pumps) i cant wait to complete it!

Or just register it ...
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Unread postAuthor: POLAND_SPUD » Sat Feb 06, 2010 10:45 am

the idea is fairly simple... you just have to build a valve that works more less like the semi auto MKIII but instead of using an external air cylinder you design the valve so one part of it acts just like an air cylinder

well basically that's something like valves used on some paintball guns....

This thing works almost exactly like the MKIII but of course it uses a spool vlave instead of the QEV. But there is an individual part on it that works as an air cylinder and looks like it
Image


but there are a lot of valves that are even simpler than that... I guess that this one is fairly simple
Image

this is also fairly simple and should offer good flow
Image
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