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1/2" bore 3/4" copper coaxial musket

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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1/2" bore 3/4" copper coaxial musket

Unread postAuthor: absinthe » Tue Aug 18, 2009 7:03 am

i just finished my newest gun

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its a bit long (barrel is 120cm) but i think thats alright for a musket :P
it has a few changes to be done (different blow gun this one leaks at 200psi) and removing the ball valve, because the barrel is so long inside the outer it flopped around, to remedy this i put 3 small blobs of solder on the outside of the barrel and filed them down so the steady the barrel works great (its the only solder in the gun i didn't want to be fixed to a length, or anneal the pipe) ..

the piston is dam fast, after allot of playing around i found that a tap washer fits in the back of a 3/4" male threaded copper olive fitting (see below although thats a 1/2" one) and using a bolt to go the pipe stop in the middle of the fitting and some soft rubber and a washer on the face it works great.. (and no epoxy leak free at 220psi)

(copper olive)
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(piston in olive fully open from rear)
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(piston fully open front)
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(piston fully closed front)
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(piston fully closed back)
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(tap washer bump stop)
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no leaking and very sensitive even with the larger than it needs to be pilot (removing the ball valve will shrink it some)

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Unread postAuthor: jackssmirkingrevenge » Tue Aug 18, 2009 7:18 am

Looking good :) Why not cut off that extra bit of bolt at the back of the piston, less weight and it will accelerate faster ;)

The blowgun can be expected to leak at some point since most of them rely on pressure to keep closed - be careful as if it fails, it could result in inadvertant firings.

What are you using as ammunition, and where are the damage pics :P :D
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Unread postAuthor: jmadden91 » Tue Aug 18, 2009 7:30 am

Looks beautiful mate. You have a quick connect on the blow gun, you could use that to fill if you simply hold the trigger open. That way, you could get rid of the whole Tee, not just the ball valve.

Again congratulations on a beautiful gun :)
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Unread postAuthor: FORE!!!! » Tue Aug 18, 2009 7:34 am

not a bad idea jmadden,altho where will the piston be housed?
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Unread postAuthor: absinthe » Tue Aug 18, 2009 7:37 am

i will be removing the extra bit of bolt but i wanted to make sure she was working right before i did that (it can be dam hard to get the nut back on after cutting sometimes :P) the blowgun leaks cause its run in reverse i will be changing the type so i don't have to run her back wards.. at this stage i am using bolt for ammo and having better result than i expected lol

from about 6 mtrs i fired a bolt at my side gate at about 180psi. i was expecting it to just bounce off..
(front you can see the bolt thread)
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i was wrong, a few more psi and i think it would have been through.
(back)
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Unread postAuthor: jmadden91 » Tue Aug 18, 2009 7:38 am

It wouldn't move, it would still be housed in the 3/4" Nipple. He would simply move the union connecting the ball valve to the tee and use it to join the nipple directly to the reducing bush connecting the blow gun. Resulting in minimal pilot volume.

Off topic:
@FORE!!!: You ordered a scope for your gun right? Did it come from overseas? I ordered mine some time ago and im still waiting. Im hoping customs didnt have a problem with it :?
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Unread postAuthor: absinthe » Tue Aug 18, 2009 7:49 am

the front of the piston is housed inside the piece of 3/4" copper pipe and the back inside the fitting.

i did have the air on the blow gun but it was kinda annoying. lol and for the piston to work i would still need to use a female to female adaptor instead of the T

i think i will use a compressor disconnect instead (a female one so it seals) and make an adaptor that has the ball valve in it so i can use the gun with the compressor still attached, or charge and walk away[/quote]
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Unread postAuthor: jackssmirkingrevenge » Tue Aug 18, 2009 7:58 am

absinthe wrote:from about 6 mtrs i fired a bolt at my side gate at about 180psi. I was expecting it to just bounce off.


An elementary issue with homebuilt launchers, never underestimate the power of your launcher :wink:

Try wrapping the end of the bolt in tape (say for 1" wide tape, have 1/4" at the end of the bolt and the rest past it), it will fly straight and give consistent penetration.
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Unread postAuthor: Ragnarok » Tue Aug 18, 2009 8:29 am

jackssmirkingrevenge wrote:An elementary issue with homebuilt launchers, never underestimate the power of your launcher

My default state is to act as though it WILL wreck whatever I'm firing at.

99% of the time, the assumption is right.
The important 0.1% of the rest is where I underestimate what "armour piercing" means.

EDIT: Better phrasing.
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Last edited by Ragnarok on Tue Aug 18, 2009 6:58 pm, edited 1 time in total.
Does that thing kinda look like a big cat to you?
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Unread postAuthor: absinthe » Tue Aug 18, 2009 8:34 am

i know that now :P i should have guessed it would do that.. i mean i shot a spud through an oil drum with my fire extinguisher cannon today as well and i didn't expect that :P
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Unread postAuthor: far_cry » Tue Aug 18, 2009 5:48 pm

hey.. nicely done hell of art you have there

try shooting some dart with it

and the piston , i think you should make it like a cylinder
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Unread postAuthor: absinthe » Tue Aug 18, 2009 6:50 pm

why would i want to make it a cylinder? that would just add more friction...

and also be very hard to seal as the hole in the middle of the brass fitting would need to be drilled and that would reduce the bump stop to 0 i think this works just fine..

we will see how it goes at 400psi but i think it should be right (although i may need to change the sealing surface)
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Unread postAuthor: starman » Tue Aug 18, 2009 6:58 pm

Very solid coax there. Nice design and presentation!
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Unread postAuthor: ramses » Tue Aug 18, 2009 8:21 pm

That looks great, but the blowgun is in backwards, and that is why it is leaking. Most people will put hook the inlet of the blowgun to the pilot port. This allows the pressure to actually hold the blowgun closed. With your blowgun, that would be rather awkward to fire, unless a hose was used.

You could possibly take apart the valve and replace the spring inside with a stronger one to be able to keep the blowgun in the current position.

To optimize performance, you might be able to fill the cannon with air through the blowgun and replace the tee with a coupling. The extra bolt length could be cut off and the nuts could be loctited in place.

Other than that, the cannon looks great!
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Unread postAuthor: jackssmirkingrevenge » Tue Aug 18, 2009 9:37 pm

ramses wrote:That looks great, but the blowgun is in backwards, and that is why it is leaking.


*cough*

JSR wrote:The blowgun can be expected to leak at some point since most of them rely on pressure to keep closed - be careful as if it fails, it could result in inadvertant firings.


*splutter*

absinthe wrote:the blowgun leaks cause its run in reverse I will be changing the type so I don't have to run her backwards


;)
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