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Pcp pellet/bb gun (closed,see new thread for build log)

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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Unread postAuthor: sinister_shadows » Mon Feb 18, 2013 10:19 am

The qev, 3way and the push to connect fittings im using are all rated to 150psi. i dont know if they would hold up to the 450psi with that setup.

my end goal is to wire up a timer switch thing (when i can figure out how) to the solenoid, allowing me to have fire mode selection between semi and auto, so if the fire chamber is to large it wont fill to 150psi quickly enough.

gun is being powered by greengas also, not co2, was just thinkin of paintball tanks when i posted :P
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Unread postAuthor: jackssmirkingrevenge » Mon Feb 18, 2013 10:23 am

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Unread postAuthor: sinister_shadows » Mon Feb 18, 2013 10:46 am

pack of 12 for 50$ isint bad. Any idea of the dimensions of it? its either gotta be in a backpack, or small enough to fit in the buttstock of the styre.

Useing those cylinders, is there no need for a firing chamber? just hook that straight to the qev? (for both semi and auto)

Which connections do i use to connect the cylinder to the qev (if on the inside i would also need a small tap to turn it on and off somewhere discreet)

the qev has 12.5mm ports, and im using 8mm tube with push to connects for everything so far.

Sorry for all the questions, just want to get it right the first time :D
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Unread postAuthor: dewey-1 » Mon Feb 18, 2013 3:18 pm

Here are dimensions for a typical 14 ounce cylinder.
Home Depot has them (BernzoMatic) for about $3 each.

edit: added 16 ounce cylinder
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Unread postAuthor: mark.f » Mon Feb 18, 2013 3:29 pm

Something to consider using propane is weather. If you live in a cold climate it could reduce pressure significantly. You'd need a tank temperature of about 90 degrees F to get your 150 PSI, and that's before tank cooling during firing.
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Unread postAuthor: Zeus » Mon Feb 18, 2013 4:43 pm

Since you're in Aus, don't use those cylinders. I feed my blowtorch with them, and they go for about $24 at Bunnings, cheapest I've ever seen them is $12 at the Elmore Field days. You can get those fat boy propane canisters for $10 at all the camping shops, but they don't fit a stock too well.

You're better off building a small internal tank, and filling it from an exchanged 9kg tank. That's about $21 for a swap, so $0.50 for every pound, as opposed to $10 every pound in disposable tanks. I'm just using a straight 9kg tank for the airsoft M2 project I've been playing with for the last month or so.

Research refilling propane tanks for info on it, I do it with small camping tanks, you only need about $20 worth of fittings. Big W sell a POL (LPG tank fitting) to male 3/8" LH (left hand), and a female 3/8" LH to 1/4" NPT. Then just make up a short line from solid vinyl tubing, and hook it up to the gun. You just have to put in a purge valve to let the propane flow in, and invert the LPG tank. Really simple.
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Unread postAuthor: sinister_shadows » Tue Feb 19, 2013 6:37 am

The idea of a building a small tank on the inside that you fill with liquid propane i like alot. would allow alot of shots and a custom size. What would you make the tank from, or would you get a shop to do it for you. Id presume the tank would also have to be vertical, so you get gas not liquid into the 3way.

I had a look for a purge valve but found alot of results of different things.
what sort fittings you would use on a small built tank? never built a pressure vessel to hold liquid propane.

i found the fittings to go from POl to 1/4 fitting also, have on sitting on my desk with a normall QD on it, but will replace it with a push connect with a nylon line
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Unread postAuthor: jackssmirkingrevenge » Tue Feb 19, 2013 7:00 am

sinister_shadows wrote:The idea of a building a small tank on the inside that you fill with liquid propane i like alot. would allow alot of shots and a custom size. What would you make the tank from, or would you get a shop to do it for you.


Look for small fire extinguishers, many are thrown away because they expire but they would still hold pressure perfectly well so you could get them cheap.

Id presume the tank would also have to be vertical, so you get gas not liquid into the 3way.


You could use an anti-siphon tube.

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Unread postAuthor: Zeus » Tue Feb 19, 2013 7:04 am

Steel fittings will do the trick, and look at anti syphons for CO2 tanks, same thing. I reckon a 3/4 by 6" would suffice as a chamber.

A needle valve will do the trick to purge, a propane tank uses a small bolt with a rubber sealing face. Something to consider is that liquid propane is a fantastic solvent, and will dissolve some plastic parts, and deposit it elsewhere. Choose the plastic parts wisely.
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Unread postAuthor: sinister_shadows » Wed Feb 20, 2013 10:40 pm

Still waiting for my parts to show up, proably wont be till next week.

I have two things left to sort out, the internal propane tank, and something to pulse a 24v current quickly.

The internal tank i will use steel fittings like zeus recommened, though i need to try and find someone that has done something like it,to give me a good idea on how to build it. Ive found this anti syphon thingy, i just have no idea what fittings use with it (i just cant seem to get my head around this tank)

http://www.ebay.com/itm/Paintball-Anti- ... 588aca8fec

So im left to find something that can quickly switch 24v dc on/off (~0.25s). Will something like this do the trick? looking for something that i can adjust to get the best rof while still feeding reliably

http://www.ebay.com/itm/DC-24V-8-Pins-D ... 35c394cd85

It will be hooked up to this, in hopes to get select fire

http://www.ebay.com/itm/380530075392?ss ... 1497.l2649

And thanks so much for the help so far guys, you and the forum have been invaluable to this build. Will be handing out credit and cookies when its done ^_^
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Unread postAuthor: Zeus » Wed Feb 20, 2013 11:25 pm

The anti syphon is just a tube that's bent up inside the tank, so that it's out of the liquid propane. Really simple. You don't even need it if you have the tank outlet upright.

You won't get select fire from that timer, plus it's really bulky. Look up 555 timers, and how to use them as a monostable (one shot every time it's triggered) and an astable (keeps firing until disconnected). It's the easiest way of going about it without turning to microcontrollers.
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Unread postAuthor: sinister_shadows » Wed Feb 20, 2013 11:36 pm

To clarify, all that timer needs to do is full auto (send a signal every 0.25s), for semi fire i just flick a switch that sends 24vdc straight to the solenoid, bypassing the relay. I looked into 555 timers, did my head in :P

bulk isint really and issue with it, i have a decent ammount of space to mount it, just needed to make sure that it repeats the signal while 24v source switch is held in. Electronics are not my strong point
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Unread postAuthor: Zeus » Wed Feb 20, 2013 11:41 pm

That timer won't give you full auto, it'll give you a regulated pulse every time you trigger it, but it won't repeat.
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Unread postAuthor: sinister_shadows » Wed Feb 20, 2013 11:51 pm

Ah I understand. Well I guess its time to hurt my brain with 555 timers >.<

Cheers for letting me know its not want I want
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Unread postAuthor: Zeus » Wed Feb 20, 2013 11:55 pm

Since you're in Aus, checking these out would be a good idea.

A 555 kit

Instructions for it

You can just replace the capacitor and resistor to your needs, how to do it is in the instructions.
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