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high velocity burst disc 6mm pneumatic

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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high velocity burst disc 6mm pneumatic

Unread postAuthor: jackssmirkingrevenge » Sat Sep 08, 2007 1:20 am

Not sure if this should be in the hybrid section, as that's what I intended this project to be - here's the original design idea, but I was doing some routine air testing and this was the velocity (according to my Combro CB-625 that has been tested against other chronies at over 1300 fps so I have no reason to doubt the result) I got for a 0.12 gram BB :shock:

Image

I was trying to see at what sort of pressure different discs would burst, and quickly discovered that across a 6mm diameter area, it's pretty high. With a single layer of ordinary transparent tape, it held right up to the maximum pressure I could give it with my shock pump (around 400 psi) and only burst when I unscrewed the fitting slightly. I ran a BB through the chrony and got 1032 feet per second, so I tried again, hence the above result :D

I was going to try it as a hybrid but to be honest I think I'd rather do some more high pressure air tests for now. Here's the completed breech with an inch tape for scale:

Image

It's interesting that in spite of the smaller chamber than the final version of my HVBB project, the velocity with 0.12 gram BBs is much higher - clearly some sort of valve bounce is the problem. Enough of that, I have more holes to make :D

As always, for more detailed information on using epoxy, check out the how-tos here and here.

edit: videos in action

[youtube]http://www.youtube.com/watch?v=lMWNpiaPha8[/youtube]

0.25g BB at 1017 fps straight through a steel (empty!) lighter fluid can

[youtube]http://www.youtube.com/watch?v=t0OnQZvvR7g[/youtube]

0.12g BB at the same can, only penetrated one side. Sadly the chrony didn't get a reading.

[youtube]http://www.youtube.com/watch?v=jiw_r_IxSEE[/youtube]

0.25g BB at 982 fps straight through a plastic toy container
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Last edited by jackssmirkingrevenge on Thu Oct 16, 2008 3:24 am, edited 2 times in total.
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Unread postAuthor: hi » Sat Sep 08, 2007 1:23 am

i wonder if that would hurt...

thats very cool. i think making it a hybrid would be very hard.
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Unread postAuthor: jackssmirkingrevenge » Sat Sep 08, 2007 1:50 am

hi wrote:i wonder if that would hurt...


I don't think you'd be very popular on your local skirmishing ground :D

I just tried with a 16 grain 0.22 airgun pellet and got 720 feet per second - that's a very healthy 18.4 ft/lbs :)
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Unread postAuthor: wannabie » Sat Sep 08, 2007 1:52 am

wow thats really fast lol.

yeah i think it would be hard to make into a hybrid but if you could get it to work it would be worth it.
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Unread postAuthor: jackssmirkingrevenge » Sat Sep 08, 2007 2:21 am

As usual (honestly, when will I ever learn?) I've put it under too much strain and it's sprung a leak. I've removed the rear section, screw the hybrid, I'm rebuilding it as a pure pneumatic for high speed testing.
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Unread postAuthor: wannabie » Sat Sep 08, 2007 2:26 am

OH NOES mabye ill just have to make a 6mm hybrid... hmmm mabye...

Oh well i look forward to seeing the result of you rebuilding

BTW how long is your barrel?
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Unread postAuthor: jackssmirkingrevenge » Sat Sep 08, 2007 2:34 am

wannabie wrote:OH NOES mabye ill just have to make a 6mm hybrid... hmmm mabye...


If you can get your hands on the right materials, I don't see why that should be a complex undertaking.

BTW how long is your barrel?


37 inches
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Unread postAuthor: wannabie » Sat Sep 08, 2007 3:07 am

37 inches... thats like nearly a meter right?
is your barrel 9/32's or somthing?
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Unread postAuthor: jackssmirkingrevenge » Sat Sep 08, 2007 3:09 am

94 centimetres, my barrel is 7mm O/D 6mm I/D brass tube.
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Unread postAuthor: spud yeti » Sat Sep 08, 2007 3:10 am

wow, nice speeds! I agree that you should just screw the hybrid and make a pneumatic :D
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really good quote/phrase here
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Unread postAuthor: experament-u2 » Sat Sep 08, 2007 3:24 am

jackssmirkingrevenge wrote:As usual (honestly, when will I ever learn?) I've put it under too much strain and it's sprung a leak. I've removed the rear section, screw the hybrid, I'm rebuilding it as a pure pneumatic for high speed testing.


:(
oh well its very impressive for a pneumatic and i would love to see a video of it shooting

good luck with fixing it and getting it to shoot faster and better
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Unread postAuthor: jackssmirkingrevenge » Sat Sep 08, 2007 3:30 am

experament-u2 wrote:oh well its very impressive for a pneumatic and i would love to see a video of it shooting

good luck with fixing it and getting it to shoot faster and better


It's already curing, I'm going to leave it till Monday to make sure it's completely cured, I'll definitely make a few videos afer that :)
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Unread postAuthor: wannabie » Sat Sep 08, 2007 3:30 am

jackssmirkingrevenge wrote:my barrel is 7mm O/D 6mm I/D brass tube.


Hmm thats odd, when I went to my local hobby shop to see if they sold brass tubing they did, but it was all mesured in imperial...
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Unread postAuthor: jackssmirkingrevenge » Sat Sep 08, 2007 3:40 am

Joys of living in Europe :) 9/32" is around 7mm, so it could be close. Best thing is to take a vernier caliper or actual BB with you to the shop to see what fits well.
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Unread postAuthor: wannabie » Sat Sep 08, 2007 4:49 am

Mabye ill just take a BB and see which one it fits best in :P
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