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New JSR semi-auto prototype (split topic)

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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Unread postAuthor: jackssmirkingrevenge » Tue Jan 05, 2010 11:29 am

JDP12 wrote:Let me get something first.. This is your prototype of the blowback with piston in the Barrel like you drew up in the previous page correct?


The green part is this (the body is part of a printer cartridge if you're wondering) while the shiny bit is the chamber.

Tested it and got some weird results, more later.
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Unread postAuthor: JDP12 » Tue Jan 05, 2010 11:33 am

Ah.. I was wondering why you were using some weird green material.. That's what threw me.

Can't wait to hear the "weird" results
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 05, 2010 11:53 am

JDP12 wrote:Can't wait to hear the "weird" results


Well, tried it at 850 psi, sealed up well enough it wouldn't fire, just vented through the pilot schrader. Took it to 400 psi with my shock pump, it did the same, until I hit 150 psi, at which point it fired. It seemed to be ok hooked up to the compressor at 100 psi, I'm worried that the flow between chamber and valve might be a little too restricted, I might try to add a little bypass.
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Unread postAuthor: Brian the brain » Tue Jan 05, 2010 1:58 pm

Eq hole must be too big.
I used about 1 mm..in a 1/2" QEV in wich the surface area of the piston is quite large compared to the sealing face.

The hole I punched was 3 mm, I had to use a plastic tube, wich I melted to lock in place to restrict the flow.
The heat made the edges swell, so it;s like a small ribbot with a tiny hole through it.
Without the molten tube restrictor it would malfunction much like your prototype..

Change your name to Hi-jackssmirkingrevenge if you have to..but show me more!!

Just so everyone knows..Jack was not the first to try the forced blowback system by recycling the muzzleblast.
The first ever to post a prototype on spudfiles was al-xg.
However, it is a very interesting system and
I'm glad JSR is giving it a try, as I will in the future.
It is the most promising auto-loader mechanism in my opinion.

Interesting... It seem kindb of... Small


Call it compact and see the genius behind it.
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 05, 2010 2:42 pm

Brian the brain wrote:Eq hole must be too big.


There's no equalisation hole, it's a solid rubber piston likethis one.

Change your name to Hi-jackssmirkingrevenge if you have to..but show me more!!


This is the thanks I get for bringing your creation back to the fore :P :D

Just so everyone knows..Jack was not the first to try the forced blowback system by recycling the muzzleblast.
The first ever to post a prototype on spudfiles was al-xg.
However, it is a very interesting system and
I'm glad JSR is giving it a try, as I will in the future.
It is the most promising auto-loader mechanism in my opinion.


Not trying to take credit here, and really it was the FX Revolution that kicked things off ;) I don't think I'll actually go that road down though, the good ol' tee-breech-and-detent system is looking pretty attractive now :) As long as I can get the bloody thing to work of course, I've added a 4.5mm diameter bypass between the chamber and the valve (because the current link is less than 1mm...) to see if it makes a difference

Call it compact and see the genius behind it.


Right up your street eh ;)
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Unread postAuthor: psycix » Tue Jan 05, 2010 6:40 pm

Maybe the rubber compresses under pressure, making your piston smaller and thus creating a gap.
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 06, 2010 2:48 am

psycix wrote:Maybe the rubber compresses under pressure, making your piston smaller and thus creating a gap.


I thought about that but both the pengun v2and the marker gunhave exactly the same piston and they work perfectly at 850 psi.

The only factor I can think of is reduced chamber flow, we'll see how the current mod works.

As to the trigger system (assuming the above works), I'm considering two options:

- A hammer valve similar to Brian's (whcih I'm presuming looks something like this that will give one burst of air per trigger pull.

- A push rod that keeps the pilot open as long as the trigger is pushed, maybe not as sparing with air but it would give a "select fire" option.

I'll test the prototype after work and see what happens.
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Unread postAuthor: MrCrowley » Wed Jan 06, 2010 3:48 am

Hmm very interesting! Strange results as well, maybe better to go with a solid plastic/metal piston with an o-ring and a tiny eq. hole or such if your mod doesn't work out.
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Unread postAuthor: POLAND_SPUD » Wed Jan 06, 2010 5:57 am

I think the solution for a multishot lies in the FX style system

well maybe it does.. I do see your point here and I am a fan of kiss principle myself

but in order to emulate what FX monson does you want to use a piston valve piloted by a hammer valve... and on top of that you want the gun to cycle using air generated to fire the shot... to do that you need to use either a double action trigger (to cock the hammer) or use the energy of air generated to fire the shot

as you can see now it doesn't sound as simple as it did in the past :wink:

so, jsr, do you plan to build a proper machined version of this if it proves to work the way you want to ?? (i.e. to you want to build a proper HPA version of this design??)


what I think is the simpler solution is to machine the main valve like the one in 'hpvalve-with-hp&lpcircuits.PNG'...
the valve could be built using the same technique as psycix used on the machined T he sent me...

I guess it would even be possible to combine both, the valve the loading mech and the breech into one single block of aluminium

I think that with a good design I could build a gun that runs on HPA and works as reliably as air cylinder + QEV combo...
maybe I won't be able to start the project this year but it seems like a good direction to follow
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 06, 2010 7:06 am

MrCrowley wrote:Hmm very interesting! Strange results as well, maybe better to go with a solid plastic/metal piston with an o-ring and a tiny eq. hole or such if your mod doesn't work out.


Given the similarity between this piston and other succesful high pressure projects, I don't think equalisation is the problem. The only difference is that there's a spring to aid resetting but it's quite weak so I'm not counting it as a factor. We'll see how the increased flow affects it. On the subject I'm really enjoying my new found "baking" facilities, it means I can put something together before bed time, take it with me to work the next day and it will be fully cured and ready for testing when I get home independently of the ambient temperature.

but in order to emulate what FX monson does you want to use a piston valve piloted by a hammer valve... and on top of that you want the gun to cycle using air generated to fire the shot... to do that you need to use either a double action trigger (to cock the hammer) or use the energy of air generated to fire the shot

as you can see now it doesn't sound as simple as it did in the past


I must agree that you do have a point there, it's not the easiest build - I think the simplicity I am seeing here though it that it operates from a single air supply and valve, and that it is efficient in that no extra air is being utilised. I wouldn't even think of recreating the Monsoon mechanism, especially when its further complicated by the rotary magazine.

so, jsr, do you plan to build a proper machined version of this if it proves to work the way you want to ?? (i.e. to you want to build a proper HPA version of this design??)


I'm quite enamoured with the tee-and-detent breech design, sure there's some loss of pressure from air expanding into the magazine, and it's not the most ideal for non-spherical projectiles, but the simplicity offsets these disadvantages. If I do make a gas piston design, it would purely be out of mechanical interest. If I get this working well I would certainly be interested in trying it out for a cartridge fed mechanism as illustrated here. A shell ejecting semi auto in the style of the Beretta BM59 or Clyde Barrow's shortened BAR that could put out at least 10 ft/lbs with 0.22" pellets would certainly be a bit of a holy grail for me :)

With the current prototype, if the valve works the plan is to turn it into something which looks like suppressed Tec-9 firing either 0.177" BBs or 0.22" pellets from a spring loaded magazine feeding into a tee breech.

edit: No go, the bypass didn't change a thing. I don't want to give up on this though, bigger piston perhaps?
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Unread postAuthor: Brian the brain » Wed Jan 06, 2010 1:11 pm

The spring, wich you think is too weak..DOES NOT PLAY A ROLE in shutting the valve after a shot!

Trust me..I tried it without a spring and there was NO difference.
It is merely there to keep the valve shut during pressurisation from 1 atm up.
Without it I had to put my hand over the barrel port and pull it away, making the piston close the port.
As soon as I reached about 2 bar, it worked exactly the same as without the spring.

The issue is not having an eq hole..

another thing might be..how smooth does the piston move??
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 06, 2010 2:10 pm

Brian the brain wrote:The issue is not having an eq hole..

another thing might be..how smooth does the piston move??


There shouldn't be a difference between an equalisation hole and a slightly loose fitting piston. It moves easily enough too. If anything piloting the piston and not getting a firing is a sight of too much equalisation. It could be piston flexing, there's a lot more travel when compared to my other projects.

I'm stumped, I was thinking of taking a different approach. No spring, and the main chamber feeds into the pilot chamber through a fine line which then feeds into the firing chamber, as below:
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Or what the heck, I should just lose the main chamber and make lots of these!
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Unread postAuthor: JDP12 » Wed Jan 06, 2010 4:05 pm

Well wait...

So the basic idea is to hVe this thing fire yet automatically refill from a source... Correct?

And now your plan is to do it via a thin line of some sort..

I like the idea... I haven't gotten semi- auto to work in the past.

However, the problem I see is that the firing chamber will just get dumped via the pilot schrader.

If you did the last picture.. Wouldn't that just be a repeat of your endeavors into a pneumatic cartridge?
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 06, 2010 4:14 pm

JDP12 wrote:However, the problem I see is that the firing chamber will just get dumped via the pilot schrader.


Why?

If you did the last picture.. Wouldn't that just be a repeat of your endeavors into a pneumatic cartridge?


Still want to make it work at some point ;)
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Unread postAuthor: Brian the brain » Wed Jan 06, 2010 4:17 pm

This new idea resembles Psy's set up on the QEv-pop-off
He too pilots it whilst air is coming in behind the piston.


It works...so..
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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