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New coax idea?

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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New coax idea?

Unread postAuthor: YEAHADD16 » Tue Dec 27, 2011 8:40 am

I was messing around with some of my guns, and I really want to build a break action shotgun, something that looks legitimate and functions somewhat to the real thing

I figure building a coax is as compact as I can get, but I also want it to be breach loading. I don't know if this is possible, but this is the idea i have shown below.

I figure I would run it by you guys to see if this has potential, if not, eh, just got to keep crackin at it :lol:
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The plug in the breech would be removed to load the gun. This picture is off scale, but i was thinking that from the piston back, would only occupy 2, maybe 3 inches
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Unread postAuthor: Gun Freak » Tue Dec 27, 2011 9:26 am

Heh... Seems like a good idea, the physics seems sound, only thing I see is the piston would be difficult to make. You'd need tight tolerances on a lathe or ability to make female o-ring grooves.
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Unread postAuthor: Technician1002 » Tue Dec 27, 2011 9:38 am

If the breech plug were an internal piston too, it would make a much lighter piston in a QDV configuration.

The configuration above will require a huge fast pilot because as the valve cracks open and the chamber pressure drops, the pilot pressure may become higher than the chamber and close the valve instead of opening it all the way.

The pilot pressure will need to drop faster than the chamber pressure drops to prevent it.
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Unread postAuthor: Gippeto » Tue Dec 27, 2011 10:26 am

Concept is good. :)

Use rectangular ports to reduce required piston travel and minimize pilot volume. Total port area when "open" could be set ~1.25xbarrel area.

Extended probe on the breech plug to push ammo ahead of the porting is required IMO.

Keeping o-rings in their grooves at high differential pressures isn't as easy as it sounds.

Would extend the rear of the ports to behind the o-ring position with the piston at its rear most travel...this will eliminate "chunking" the forward o-ring. Rounding and polishing the edges of the port will minimize slicing. Silicone grease for lube.

OR...you could try mounting the forward seal on the piston stop. Having it stay in position may also not be quite as easy as it sounds. :)


Be bloody CERTAIN to secure the breech plug. :wink:
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Unread postAuthor: Daltonultra » Wed Dec 28, 2011 12:20 am

The Gallagher rifle may prove of interest to you as a design, if you can find anything on the action.
Image

The Gallagher is really strange, as it is a lever-break action. When the lever swings forward, the barrel first slides forward, opening the breach, and then drops downward like a break-action shotgun.

Using an action like that, you could actually design the gun so that the piston and valves are in the rear half, and the barrel and chamber seals are in the forward half. If the barrel end is male, you could easily design it as a breach loader. But it would take some design work to get the linkage right.



(The other weird thing about the Gallagher is that the breach actually open at the middle. The bullet sits half sticking out of the breach, and then slides back into the rear half of the breach when it closes. And the entire round is capsule-shaped. And instead of having a primer built into the bullet casing, it just has a hole in the back, and uses an old cap-lock to set off the round. Truly odd...)
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Unread postAuthor: POLAND_SPUD » Wed Dec 28, 2011 3:26 am

I agree with technician on this...

build a small version of his QDV with a spring loaded piston

you cock the gun by pushing the bolt forward and the valve is held in closed position by a sear, as soon as you pull the triggger the valve retracts and the gun fires
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Unread postAuthor: YEAHADD16 » Wed Dec 28, 2011 5:54 pm

Thanks for the advice, i need to do a lot more research and prototyping, i like QDV bolt idea a lot, and the lever/break action looks really cool.

I was thinking of other ways to turn a coax into semi auto and I was wondering if this has been tried

The chamber would have to be big enough to hold the T connection and then boring ahole through the chamber might not be the best idea, but at low pressures and a pant load of epoxy or jb weld i think it could be made airtight
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Unread postAuthor: Gun Freak » Wed Dec 28, 2011 6:26 pm

Sorry but that idea's been proposed many times :D

Instead of putting a hole in the chamber, you could put a tee on the chamber and put a bushing in the side port for the magazine. I've drawn it before... I guess it could be done.
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Unread postAuthor: YEAHADD16 » Wed Dec 28, 2011 10:43 pm

:roll: duh, why didn't i think of that :lol: makes sense. does it seem practical though, might as well use a qev or something. Thing is I what it to be compact and yet simple
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