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Mini Breech loading Coaxial build & ideas

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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Mini Breech loading Coaxial build & ideas

Unread postAuthor: kablooie » Mon Mar 17, 2008 11:17 pm

This design is nothing new, although I have not seen a mini verion of it, it is a mini breech loading coaxial design. The cannon breech loads through the tee, and is made with galvanized steel pipe fittings and malleable iron fittings. The majority of it is 3/4" pipe, although the tee is 1 1/4" to allow the 1/4" tee to fit inside.
I will be making heavy use of epoxy (cross your fingers, I have not used it like this before) to attach the brakeline to the galv. pipe, unless of course there are some relatively inexpensive fittings to the the job. The diagram pretty much explains itself otherwise, but some basics are:
3/4" epoxy piston
1/4" brake-line barrel
Breech loading
Blowgun exhaust

Things I have yet to get:
1/4" threaded schrader
1/4" brakeline
Shock Pump
Probably some other not as important stuff too.

Questions and advice are welcome.
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Attachments
BB coaxial.jpg
Hopefully this will be self explanatory, one thing I have not quite figured out is how to only let 1 bb at a time in through the ball valve (maybe by doing some modification)
BB Coaxial pic.jpg
Basic pic, loosely assembled.
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Unread postAuthor: psycix » Tue Mar 18, 2008 7:40 am

I guess that would work just as expected.
Cant wait to hear if it worked :)
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Unread postAuthor: FeLeX » Tue Mar 18, 2008 7:50 am

Looks pretty good so far. Seems like it could take realy high pressure ;)
If it was me though I would have a bigger barrel.
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Unread postAuthor: kablooie » Tue Mar 18, 2008 9:33 am

Thanks for the replies, hopefully it should work, my main worry though is leaks through my epoxy bonds, but I should be able to avoid those.

The barrel is not drawn to scale in the diagram and is not present in the picture. It will extend about 2 feet from the chamber, so hopefully that will be enough.
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Unread postAuthor: kablooie » Tue Mar 18, 2008 9:12 pm

I have come across another problem, and was wondering if you guys have any advice. The inside of the 3/4" galvanized steel pipe is quite rough, and Counterstriker tried unsuccessfully to cast an epoxy piston in it and it got stuck in the pipe.

One possible solution to this problem would be to use 1" galv. pipe instead of 3/4" and then sleeve 3/4" pvc (sanded to fit) inside that pipe to house the piston. This would make sure there would be absolutely no flow restriction. I am tempted however, to use 1/2" pvc and to make sure that it does not encase the end of the barrel. This would be a little bit tricky though, because everything is threaded, so after I tighten it all the barrel could be too far forward, causing big time flow restriction. Here is a diagram:
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Piston sleeve small.jpg
Self explanatory.
Piston sleeve small.jpg (24.65 KiB) Viewed 736 times
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Unread postAuthor: psycix » Wed Mar 19, 2008 8:11 am

Well it seems possible to me.
Just make sure you get things measured out well.
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Unread postAuthor: kablooie » Wed Mar 19, 2008 11:36 pm

I'll be sure to tighten everything before I sleeve that 1/2" pipe. Anyone else have any advice? Some of the epoxying worries me.
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