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Gas Sampling Cylinder PB Rifle #2 (Semi Auto Blowback)

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Gas Sampling Cylinder PB Rifle #2 (Semi Auto Blowback)

Unread postAuthor: Tetsuo315 » Sat Jul 08, 2006 2:11 am

This is my second pneumatic to use a sampling cylinder. In this post I won't be talking much about the velocity, kinetic energy, and what not. If you are interested in the specs, check out my first post "Gas Sampling Cylinder PB Rifle". This cannon is similar to my other one, So most of the specs are the same.

First of all I can't fully claim this as my own. I did see a chamber set up like this one on this sight that dealt with semi auto by Mr. Plow. However, that post did not go in too much detail as to what or how those tubes and regulators were used. So I made my own version :D. I first had to figure out the action. I used 3/4" CPVC inside 1" CPVC. The 3/4 " is just the right size with enough clearance to slide inside 1". Check the diagram below.

The chamber section has an additional secondary air tank made from sch 80 PVC. It stores air at a certain pressure to blowback the action. The gauges might seem confusing, so here is their purpose back to front. The first gauge tells me the overall pressure of the cannon. The second gauge is a regulator to limit how much air gets into the second chamber.
The third gauge is a flow control. When you reduce pressure on a regulator or the air going into it, it equalizes the air or gas and bleeds some of it off. The third gauge with the flow controll slows down the air leaving the secondary chamber. That way there is still enough pressure left to recycle the next round. see picture for details.

There is a second blowgun on the cannon. It acts as a valve to the homemade air ram on the side of the barrel. It is setup to release air into the air cylinder after the cannon has fired. I know there are otherways to get semi auto, but I do not have access to a decent lathe. So this is the methond I chose. Anyways here are a collection of pictures of the setup
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Attachments
Action Close Up.JPG
Note the acrylic rod. It is used as a piston to blowback the action
GAUGES AND REGULATOR SETUP.JPG
ChambersandValveSetup1.JPG
This thing gained some weight once I put all of the gauges on
Barrel Setup.JPG
This diagram shows whats going on inside the barrel and action
Gas Sampling Ctylinder No 2.JPG
My new creation
Damage.JPG
Ah yes, we must show damage :).
Last edited by Tetsuo315 on Sun Jul 09, 2006 3:17 am, edited 6 times in total.
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Unread postAuthor: )DEMON( » Sat Jul 08, 2006 2:49 am

Again this is amasing,you have done an outstanding job.What is the rate of fire? I would like to see some damage pics.
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Unread postAuthor: Benny » Sat Jul 08, 2006 3:35 am

Awesome. So you have a first chamber and then a regulator and then a smaller chamber, and the first chamber fills the second, and then you fire and this cycle repeats?
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Unread postAuthor: rna_duelers » Sat Jul 08, 2006 5:02 am

Thats amazing,i was waiting for this cannon.Any ideas on the fps its reaching?Not as high as the one from before i would think,What psi do you run it at?
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Unread postAuthor: Tetsuo315 » Sat Jul 08, 2006 12:25 pm

The metalic chamber fills with air to 135 PSI, the second chamber is regulated to 60 PSI. When the cannon is fired all of the air in the first chamber is expelled propelling the paintball @ appox. 750-812 FPS. The second chamber stores up enough air to blow back the action. Since the regulator is not a check valve, air in the second chamber will start to escape. Since I could not find a check valve at my local hardware store, or feel like ordering one, I use a flow control valve to slow the air leaving the secondary chamber. This also slows the air filling the chamber, but not by much. The flow control is under the third gauge. I'm not sure on the rate of fire, but it is close to 2-3 per second. The hopper pictured on the gun can hold 9 PBs. It was just a piece I had cut that was lying around, so I was not concerned with how many I wanted it to hold. When in use, it is connect to a constant air source.

As for damage pics, I will try to post some. I can say that this gun is similar in power to the other one I made. It shattered 1/4 acrylic with no problem 40 feet away
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Last edited by Tetsuo315 on Sun Jul 09, 2006 12:56 am, edited 1 time in total.
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Unread postAuthor: saladtossser » Sat Jul 08, 2006 4:44 pm

WHOA
Mr.Plow eat ur heart out
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Unread postAuthor: CpTn_lAw » Sat Jul 08, 2006 5:36 pm

outstanding job here mate....
When you say that you put 135 psi in this, is it safe for the valve? many people told to me that it should be safe to use 110 psi at max for sprinkler valves...cuz, if it's safe, i'm going to do so, my metal chamber and metal barrel will take advantage of the higher pressure...imagine a marble fired at 135 psi....
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Unread postAuthor: Tetsuo315 » Sun Jul 09, 2006 12:50 am

The gas sampling cylinder is rated over 1000 PSI so no worries there.
A 1" Rainbird sprinkler valve is rated up to 150 PSI. Since its air we are talking about and not water, I won't take it any higher than 135 PSI. In the future I would like to go with a metal sprinkler valve or a QEV. I don't know about you guys, but the thought of pressurized plastic 6 inches away from my head exploding does not look so good :?. Exploding metal is not good either, but at least it will hold up better than plastic.
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Last edited by Tetsuo315 on Mon Jul 10, 2006 2:00 pm, edited 1 time in total.
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Unread postAuthor: rna_duelers » Sun Jul 09, 2006 6:23 am

2-3 per second~bows~Thats crazy and at and avergae of something like 800fps that thing is lethal.Have you chrony graphed this gun or is that using the ggdt to find the fps?This is one of those cannons that a spudder has spudding dreams over.I'm bulding my newest cannon at the momment and i would like figures of 800fps n such but i just cant see it happening cuz my cannons suck!
Nice cannon...I think im pitching a tent over it :shock:
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Unread postAuthor: Tetsuo315 » Sun Jul 09, 2006 8:10 am

Last night when I shot it, it was more like 1.2-2 a second. When I posted my first gun GGDT quoted my FPS @ 812. I took the specs for a 1" sprinkler valve off the GGDT site. I dumbed down the specs a little. Rainbirds open slower than Watermasters. And the specs came back as 812. like I said about my first gun, that seems slightly optimistic. I won't know for sure until I get ahold of my grandfathers chronograh. Based off the damage done to the 1/4 acrylic, I can say I would not want to get hit by a paintball at that speed.
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Unread postAuthor: Tetsuo315 » Sat Aug 26, 2006 9:26 am

Today I will be testing the FPS with a chronograph for both versions of the pneumatics I made. Time to see just how accurate GGDT is. I will post the results for both guns later today.
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Unread postAuthor: Kris.Is.Awesome » Sat Aug 26, 2006 2:49 pm

Wow- AMAZING gun!

What would it cost to build one for myself?
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Unread postAuthor: Tetsuo315 » Sat Aug 26, 2006 3:21 pm

GGDT calculations were not very close with this gun I chronographed the velocity at an average of 650-663 FPS. I did not take the actiion/bolt section into consideration when pluging in the numbers. It constricts the flow of air. I'm not disapointed at these results. this just tells me I need to improve the semi-auto action. 650, 800 I still would not want to get hit by a PB from this gun. So there you have it, a more realistic number :) I will say at this time that GGDT was not at fault but my own human error element. GGDT after all is a tool to help us get more potential out of our projects.

As for the cost to make something like this $80.00 thats excluding the metal chamber.
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Last edited by Tetsuo315 on Sat Aug 26, 2006 3:27 pm, edited 1 time in total.
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Unread postAuthor: singularity » Sat Aug 26, 2006 3:25 pm

i cannot seem to find your first gun when i search "Gas Sampling Cylinder PB Rifle" so i wnat to ask about the barrel setup diagram, is that a picture of the gun at rest or is it while its blown back
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be sure to check out my <a href="http://www.spudfiles.com/forums/ak-style-airsoft-vortex-gun-t10959.html">AK Styled Vortex Gun</a> and my <a href="http://www.spudfiles.com/forums/at-4-t9627.html">AT-4 Rocket</a>

upcoming projects... finalized clip fed BBMG and ball point pen sniper
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Unread postAuthor: Tetsuo315 » Sat Aug 26, 2006 3:29 pm

blown back position.
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