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First Airgun

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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Unread postAuthor: Gun Freak » Mon Feb 28, 2011 8:08 pm

Just take your extinguisher over to a store that sells fittings and see if there are any standard sizes that fit. Then you know for sure which one to buy.
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Unread postAuthor: Alster370 » Wed Mar 02, 2011 3:30 pm

Well we tried a 28mm and it was a tad too big, so I will take it down to PTS and see if they have anything suitable. If that fails I thought about using metal epoxy to "weld" it on.

Im also going to adapt it to use a homemade QEV. ( hot glue piston etc.) So if anyone could provide me with any recommended tutorials id be grateful.
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Unread postAuthor: Gun Freak » Wed Mar 02, 2011 7:57 pm

What I did when I found out that the threads on mine weren't standard was just cut off the fitting that came in the neck in the FE, and then I cut new threads on the inside of that fitting. It was, of course, plastic, I don't know what yours are though.

Here is a simple tutorial on building a piston valve.
[youtube]http://www.youtube.com/watch?v=vmxaI3_SJCg[/youtube]
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Unread postAuthor: Alster370 » Thu Mar 03, 2011 2:53 am

already done that with mine too, it isn't the tightest fit though so epoxy could seal that also.
I have a brass reducer that sits nicely in the threads so I might use that then epoxy the copper pipe through it, Although im not expert on epoxy myself having never had some. Yeah ive seen that video a few times, but instead of using 1" and 3/4" il use 22mm and 15mm if thats ok.
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Unread postAuthor: Gun Freak » Thu Mar 03, 2011 5:35 pm

Yeah, any size will work.
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Unread postAuthor: Alster370 » Sat Mar 12, 2011 7:39 am

Well i managed to attach that fire extinguisher and the performance is good. I checked GGDT and it claimed my velocity would double with a piston valve ( from ~270 to ~ 560 fps) so im going to start work on that soon enough.
Im also going down to a 8mm od barrel ( 7mm id) so I can use 6mm ball bearings as i heard that they are more accurate for smooth bore barrels. I would also like to plan a mulitshot setup of 5 shot per refill, although im not too sure how that works with a piston valve setup so if anyone could shed some light on that I would be very grateful.

Here's how it looks a the moment, ugly but functional:

http://s785.photobucket.com/albums/yy14 ... =003-3.jpg

oh and im going to reposition the tank to act as a stock, so that its behind the barrel.
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Unread postAuthor: jackssmirkingrevenge » Sat Mar 12, 2011 8:49 am

Alster370 wrote:Im also going down to a 8mm od barrel ( 7mm id) so I can use 6mm ball bearings as i heard that they are more accurate for smooth bore barrels.


They certainly won't be accurate coming out of 7mm I/D barrel, think golf ball in a drain pipe - it's bouncing around and no idea in what direction it's going to come out.

In terms of efficiency, the air lost past the projectile will be like having a 6mm I/D barrel with a 2mm hole drilled in the breech.
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Unread postAuthor: Alster370 » Sat Mar 12, 2011 9:05 am

See i thought 0.5mm on either side of the ball wouldn't be a problem :( the trouble is that brass has thin walls (0.45mm usually) so if i bought a 7mm pipe it would be an excellent fit (0.05mm on either side of ball bearing) but I wouldn't be able to do a compression fitting as they don't come in 15 x7mm types. So i might have to adapt an endcap or something and epoxy it.

what do you think my best option is?
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Unread postAuthor: jackssmirkingrevenge » Sat Mar 12, 2011 9:15 am

Alster370 wrote:See i thought 0.5mm on either side of the ball wouldn't be a problem :(


I know it doesn't sound like much but you have to think of it in terms of subtracting the area of a 7mm disc from a 6mm disc.

In this experiment the result I got was a 33% power loss for a 0.5mm difference between barrel and projectile.

what do you think my best option is?


obviously:

adapt an endcap or something and epoxy it


:D
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Unread postAuthor: mark.f » Sat Mar 12, 2011 9:24 am

Alster370 wrote:I would also like to plan a mulitshot setup of 5 shot per refill, although im not too sure how that works with a piston valve setup so if anyone could shed some light on that I would be very grateful.


Good trigger control, for the simplest way. Connecting the FE to a three-way valve to the piston valve which is connected to a smaller chamber would be another way. Successive shots will be weaker, though.
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Unread postAuthor: Alster370 » Sat Mar 12, 2011 10:39 am

This is what I hope to a achieve:

http://s785.photobucket.com/albums/yy14 ... tled-2.png

@mark.f

My goal is that after the pressure starts to decrease performance noticeably, a couple of pumps with the shock pump will bring it back up to starting pressure, though im not sure how many pumps will be required.

JSR: my goal was ammunition that was a good fit but could still slide down the barrel as my gun is still and will probably remain for a while, muzzle loaded. And i wasn't too sure how accurate the actual dimensions of steel balls were.
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Unread postAuthor: mark.f » Sat Mar 12, 2011 10:43 am

Alster370 wrote:My goal is that after the pressure starts to decrease performance noticeably, a couple of pumps with the shock pump will bring it back up to starting pressure, though im not sure how many pumps will be required.


Why not fill the FE to a significantly higher pressure than your gun operating pressure and connect with a regulator?

Of course, stay within the constraints of the pressure rating on the FE. :wink:
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Unread postAuthor: Alster370 » Sat Mar 12, 2011 11:01 am

well the fe pressure gauge went up to 16.5b and that was at the end of the red area so i wouldn't push it past 300psi. I have looked at regulators but they are hard to get in high pressure ratings in the uk. This is the only suitable one I have found so far.

http://www.plumbworld.co.uk/compression-pressure-0-4215

And its max outlet is 87 psi which is far too low. Im looking 300 psi to 200 psi
reduction.
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Unread postAuthor: jackssmirkingrevenge » Sat Mar 12, 2011 11:54 am

Alster370 wrote:JSR: my goal was ammunition that was a good fit but could still slide down the barrel as my gun is still and will probably remain for a while, muzzle loaded. And i wasn't too sure how accurate the actual dimensions of steel balls were.


It depends if they're genuinely 6mm bearings, or 1/4" bearings, the latter will not fit in a true 6mm barrel but still have some clearance in a 7mm barrel.
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Unread postAuthor: Alster370 » Mon Mar 14, 2011 2:23 pm

I was also wondering what the thread size/type is on those steel co2 soda stream cylinders? They are cheap for the price and if they can be fitted easily it will save me messing about keeping this FE leak proof. It will also allow higher pressures, as my FE is aluminium I believe.
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