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Semiauto WIP - blowback-study ...with homemade dcv

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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Semiauto WIP - blowback-study ...with homemade dcv

Unread postAuthor: nature-boy » Tue Feb 15, 2011 8:42 am

I am working on a 9mm semiauto with a self made 3way-valve.
Right now I am looking for an alternative of the "air-cylinder-way", that is easier and more compact (and I like moving parts at the breech :D ).

I thought that with a blow-back-breech, where the the weight of the bolt and the spring (aka rubber-band...) is tweaked that way, that the o-ringed bolt opens the mag-port just after the projectile left the barrel, similar performance could be achieved.

The self made DCV/3way-valve is made differently to most commercial sold ones and the one that MRR made. Instead of pushing the bolt in the direction of the exhaust-port, it is pulled away from it to open it, like in TECH's QDV's.
By doing this I was hoping to have some "faster-opening-QDV-style"- effect. But this seems not to be the case, because of:
a very long/heavy bolt,
three (floating!) o-ring's (much friction),
and the force of the "return-spring" (yes I know it's rubberbands...)

Here is a video of the 3way working quite well.
The blowback isn't moving in the first video because it needs about minimum 12 bar to work and a round in the barrel.
But it moves in the second one, which I will add soon (having problems with youtube...).
...I had only a hand-pump there, so I couldn't do 12 bar semi shots...
[youtube]http://www.youtube.com/watch?v=f6IUbiuIigU[/youtube]

Next thing I will do is filming the breech-action in high-speed to see if the breech is "slow enough"
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Unread postAuthor: POLAND_SPUD » Tue Feb 15, 2011 9:35 am

Nice work :)
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Unread postAuthor: Lazyboy » Tue Feb 15, 2011 9:59 pm

Looking good :)
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Unread postAuthor: POLAND_SPUD » Tue Feb 15, 2011 10:30 pm

like in TECH's QDV's
technician's QDV is just a large spool valve. Not that I think it isn't somethign cool but that's basically how all spool valves (DCVs) operate.
Well anyway, it's cool that you came up with this without knowing that in the first place - it prooves it is the right way to do stuff

"faster-opening-QDV-style"- effect
It should work like that at higher pressures
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Unread postAuthor: LovableAirGuns » Wed Feb 16, 2011 12:38 am

dude that is hell good great job :)
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Unread postAuthor: jackssmirkingrevenge » Wed Feb 16, 2011 2:22 am

Good job, any chance of the diagram of the blow-back mechanism? Are you using some sort of detent to build up pressure of just a tight fitting projectile?
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Unread postAuthor: nature-boy » Wed Feb 16, 2011 5:42 am

POLAND_SPUD wrote:...that's basically how all spool valves (DCVs) operate.

yes, but if I remember right, most commercial 3way's have the spool moving into the direction of the port that will be exposed, and most notably the spool is still balanced, in the moment/position of venting.
In the Tech-QDV-style, the spool is moved away from the port, that has to be exposed to pressure, causing the pressure to be able to push on one side of the spool additionally to the force, which moved the spool at first, so it is not balanced anymore.
Was this understandable? :?

Correct me if I am wrong with this theory about solenoids, it seems to me that you are the officially assigned person for DCV's here! :D

@jack:
no airtight detent so far and it works, but I will probably change the barrel to a slightly tighter one, where the steel balls have a perfect fit.
But my concerns are, that even without a detent the breech will move to fast... I hope highspeed-footage will show that today...
And the blow-back-breech is really nothing new, just a bolt with o-ring and a magnetic tip out of polymorph, a magnet and a sawed down nail, all glued together. I was hoping that the magnet would be enough to prevent the steel-ball to be fired out of the barrel, from the bolt pushing it, but it wasn't so I added 6mm spring-ball-detent (the small brass pipe) Here is a picture of the breech with the bolt pulled out:
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Unread postAuthor: jackssmirkingrevenge » Wed Feb 16, 2011 6:18 am

nature-boy wrote:But my concerns are, that even without a detent the breech will move to fast... I hope highspeed-footage will show that today...


You mean shoot out the back? MOAR RUBBAH BANDS :D

And the blow-back-breech is really nothing new, just a bolt with o-ring and a magnetic tip out of polymorph, a magnet and a sawed down nail, all glued together. I was hoping that the magnet would be enough to prevent the steel-ball to be fired out of the barrel, from the bolt pushing it, but it wasn't so I added 6mm spring-ball-detent (the small brass pipe)


An airtight detent isn't really necessary, once you have the ball detent in place the air coming from the valve into the bolt far exceeds any leakage past the projectile so it should still be effective.
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Unread postAuthor: nature-boy » Wed Feb 16, 2011 6:34 am

jackssmirkingrevenge wrote:You mean shoot out the back? MOAR RUBBAH BANDS :D


No, I meant the bolt will expose the mag port to soon/before the round left the barrel, causing the pressure in the barrel to drop, what will decrease performance.

And I can't use "MOAR RUBBAH BANDS", because this one is already tweaked for 12 bar, so a stronger one will cause the bolt to move not far enough to load a new round.
But maybe MOAR BOOLT MAAASS or MOAR FARICTIONN will do the trick. :D

And here is the second video showing the bolt/blowback-breech moving:[youtube]http://www.youtube.com/watch?v=bRTAKmw9UgE[/youtube]

Ah, and...hey Jack, guess what my brother said at the beginning! :D
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Unread postAuthor: jackssmirkingrevenge » Wed Feb 16, 2011 6:45 am

Nice!

MOAR BOOLT MAAASS or MOAR FRICTIONN will do the trick


Indeed :)

hey Jack, guess what my brother said at the beginning!


lol I don't know, "It's recording, go!" :roll:
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Unread postAuthor: nature-boy » Wed Feb 16, 2011 6:56 am

jackssmirkingrevenge wrote:lol I don't know, "It's recording, go!" :roll:


yes, he says "It's already recording!" ...and then: "Ehm, your foot is in the picture!"
:lol:
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Unread postAuthor: jackssmirkingrevenge » Wed Feb 16, 2011 7:08 am

nature-boy wrote:"Ehm, your foot is in the picture!"


:D :D :D
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higspeed-footage of the bolt cycling

Unread postAuthor: nature-boy » Wed Feb 16, 2011 8:04 am

Here is the highspeed-video of the bolt moving, filmed in 420 fps.
[youtube]http://www.youtube.com/watch?v=rOh6rnSAM6w[/youtube]
Although the white thing flying out of the magazine-port looks a bit like a ejected bullet-shell, it is actually the tip of the reloading-bolt, that separated from the bolt...
...not only it hit my face, now I have to make a new one... hmpf.

And as I thought before, the bolt is to fast. :(
I think will have to find a way of adding weight to the bolt to... Or does someone know a better way to slow it down???
Maybe I could use some kind of delayed blowback-system, like the ones, that are used in automatic firearms??? kind of complicated I know... :?
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Unread postAuthor: jhalek90 » Wed Feb 16, 2011 10:29 am

place a piston, about 1'' ahead of the bolt,
atatch to bolt face via a spring and guide rod.
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jackssmirkingrevenge wrote:I wonder... if you put flammable vapours inside a lady... could you get her to diesel?

POLAND_SPUD wrote:Anything is possible with the proper 3-way valve.
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Unread postAuthor: POLAND_SPUD » Wed Feb 16, 2011 11:31 am

Or does someone know a better way to slow it down???
a one way check valve and a spring... that should help to slow down the bolt on the return stroke
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