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PCP 6 shooter

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PCP 6 shooter

Unread postAuthor: LeMaudit » Mon Apr 20, 2009 9:32 pm

Hi guys,

I am not sure when my project would fit: A six-shooter gun firing small arrows, using 6 PCP cartridge :-)
Think of the 6 chambers like a Brocock cartridge (well, just the idea, not the design). Relatively small amount of air, at relatively high pressure. It would not be a replaceable cartridge, more like 6 chambers that are part of the gun.

Could vaguely look something like this nerf gun at the end, but in machined brass, aluminum and steel:

Image

Note: That's not mine, I found this beautiful paint job on Google image!

I am playing with the numbers for now, I would be grateful if someone could verify that I didn’t goofed! I am learning since a few days about compressed air, and I have little possibilities to verify if I am correct or not (and to my shame I’m not very good with math). I take the example for a single cartridge/air chamber, the 6-shooter grand scheme is for later ;-)

Here are my numbers:

- The chamber of non-compressed air would be something like 1” diameter x 3” length. That is 2.36 inch3 if I am correct.
- I plan to compress that volume to 1/8 length (like a syringe with the tip closed), that would result in 0.1 inch3 of air compressed at 338 psi.
- That means the 1” plug would have to support a 266 pound pressure.
- the air exhaust would be 1/4 inch diameter, and that is only 17 pound pressure on it for 338 psi.
- the barrel diameter would be also 1/4 inch diameter, with an equivalent length of 10 inch so that’s 0.49 inch3

Note that if I compress to 1/16" length instead of 1/8", I double the psi, but of course also the pressure on both the plug and the exhaust. That's my power/safety adjustment.

Now the big question:

If those numbers are correct, the air at 338 psi would expand to 4.6x the volume of the barrel ( 2.36 inch3 originally in the chamber that would fill 0.49 inch3 for the barrel). I suppose that would be a good kick. I have no idea how to compute velocity, but the arrow I guess would be something equivalent in mass to a 1/4 inch diameter ball bearing (steel arrow head, plastic tubing and fins.

What do you think? Stupid idea? Could work? Surely not?

:-P
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 21, 2009 12:02 am

Interesting, looks like the sort of project only a machinist would attempt ;)

For modelling performance, I suggest you download Gas Gun Design Tool, a very valuable resource.

Some diagrams of your firing mechanism would be appreciated. Is the chamber pressurised at the time of firing like a spring piston airgun or pressurised then fired through a valve?
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Unread postAuthor: mega_swordman » Tue Apr 21, 2009 12:59 am

An interesting endeavor. My only concern would be the triggering mechanism. Since you mentioned six chambers, I assume you will release this though some type of valve. Care to share your thoughts on this?

Also, with the chambers be stationary, or will the move about an axis to the firing mechanism?
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Unread postAuthor: inonickname » Tue Apr 21, 2009 3:01 am

If you wanted something like that, you could buy a shock pump, a cheap revolver cap-gun and buy some telescoping tubes and schrader valves. Then just make however many pen guns (look in the mini showcase) that will fit the chambers in the barrel (the part that revolves) and use the hammer striking on the cap gun to exhaust each cartridge..Come to think of it that would be cool..
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Unread postAuthor: psycix » Tue Apr 21, 2009 4:58 am

jackssmirkingrevenge wrote:Interesting, looks like the sort of project only a machinist would attempt ;)

Or the epoxynist.


One major problem with the rotating stuff is to get a proper seal.
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Unread postAuthor: LeMaudit » Tue Apr 21, 2009 9:17 am

Here are a few answers. I am still wondering if there will be enough compressed air to fire my arrows or if I will just make a ridiculous "pop" ;-)
Anyone care to do my math again and provide expert opinion?

I suggest you download Gas Gun Design Tool,


Thanks. I have played with GGDT a bit, but cannot configure it to mimic what I attempt. My design is more straightforward than the usual chamber/piston design I could see on your wonderful cannons, because it fire only once. Maybe I don’t know enough yet to understand it all.

Some diagrams of your firing mechanism would be appreciated. Is the chamber pressurized at the time of firing like a spring piston airgun or pressurized then fired through a valve?


Be sure I will share diagrams and plans when I prepare them for machining. For now it’s only in my head :-)
I am hesitating between the 2 options. I favor the later, pressurized then fired, because I can control the pressure, and I don’t need shock resistant materials so brass and aluminum should do. Steel is a [female doggy] to machine on my miniature equipment.

I assume you will release this though some type of valve.


Yes, but one valve (a simple exhaust?) per chamber. And I’ll start with a single chamber when I’ll build a crude prototype as proof of concept.

Also, with the chambers be stationary, or will the move about an axis to the firing mechanism?


After considering lots of “gas-factory” as we say in French for strange contraptions, I have chosen a straightforward design. But this could change, it is only a few days of thinking right now and I am open to suggestions if you have better idea guys :-)
Chambers and barrels are fixed. All the chamber exhausts are pre-aligned with all the barrels. In between there is a gap when I can slide (or rotate?) a panel between the exhausts and the barrels that have holes drilled at different positions, and sliding the panel align the hole with the chamber/barrel, one after the other. I have in mind a mechanism with a hammer that quickly move a hole in position for firing, but that is still in limbo. It is also secure, as a gas leak will not fire an arrow by mistake because of the (heavy) metal panel in between. Seal will be done with small 1/4" diameter O-rings on each exhaust and barrel end, the panel pressed in between; most certainly with a sort of tension-spring mechanism to firmly sandwich the panel but allow movement.

you could buy a shock pump, a cheap revolver cap-gun and buy some telescoping tubes and schrader valves.


Sure. But I would miss the fun. My kind of fun, machining...

Come to think of it that would be cool..


It sure would. And if it look like a beautiful Steampunk gun with shiny pieces and metal bits, to my eyes even better ;-)

Thanks for your interest guys, that's fun.
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Unread postAuthor: maverik94 » Tue Apr 21, 2009 1:49 pm

you do realize pcp is a drug....you had me confused for a moment.
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Unread postAuthor: LeMaudit » Tue Apr 21, 2009 1:57 pm

The confusion is understandable but... 6 shots? :hippy2: ???

nahh.... :shaking2:
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