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Coaxial breechload

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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Coaxial breechload

Unread postAuthor: Selador » Mon Nov 08, 2010 3:50 am

I was reading this thread: http://www.spudfiles.com/forums/viewtopic.php?t=8278&

The question was aksed: how do you breech load a coaxial?


The question was answered, but I have a different answer. And I didn't want to dig up an old thread. Seems TWTTTS get very upset about that.

And since a picture is worth a thousand words, here is my answer:
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 08, 2010 4:30 am

The problem most people (at least those not conversant with modern binary adhesives :wink:) will find is sealing the chamber at the point where the magazine pokes out.

Why not leave out the ball valve altogether and have a marble machinegun ;)
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Unread postAuthor: Technician1002 » Mon Nov 08, 2010 4:37 am

The ball valve can be modified by placing a screw inside the ball at one end and removing the 90 degree stop so it can rotate a full 360. This can make a "cup" of the ball so it will pick up a ball from the top then drop it in with a 180 degree twist. Another 90 degrees will seal the barrel for firing.

Another twist on things is to put it external to the chamber as an over/under. I know, no longer coaxial.

My solution was to put the air valve at the muzzle end of the chamber instead of the breech and then use a traditional modified ball valve breech loader.

Here is a breech loaded t shirt cannon. The valve is inside the chamber at the muzzle end of the tank. The breech loader is a slip coupling that opens the breech of the barrel for loading the t shirt.
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Unread postAuthor: MrCrowley » Mon Nov 08, 2010 4:58 am

The problem most people (at least those not conversant with modern binary adhesives ) will find is sealing the chamber at the point where the magazine pokes out.

One could use a tee fitting I 'spose. If the chamber is 2" and barrel is 3/4", either use a 2" tee with the perpendicular port 3/4" or just a 2" tee with some bushings.
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Unread postAuthor: POLAND_SPUD » Mon Nov 08, 2010 6:17 am

...or you can load ammo from behind though you'd need a special doughnut shaped piston
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 08, 2010 8:44 am

POLAND_SPUD wrote:...or you can load ammo from behind though you'd need a special doughnut shaped piston


Or throw in one of your favourite valves et voila, co-ax semi-auto ;)
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Unread postAuthor: POLAND_SPUD » Mon Nov 08, 2010 9:09 am

No air cylinders?? Heresy!! :evil:

Uhmm that would actually make a pretty cool gun. Since the whole gun is just a long tube (ohh btw you could add a silencer with the same OD as the chamber) you could easily make a nice stock for it (or just use one from a cheapo airgun)
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 08, 2010 9:42 am

POLAND_SPUD wrote:Uhmm that would actually make a pretty cool gun.


:shock:

That's twice you agreed with me in the past week - I've not checked my Nostradamus but isn't that one of the harbingers of the apocalypse?

Since the whole gun is just a long tube (ohh btw you could add a silencer with the same OD as the chamber) you could easily make a nice stock for it (or just use one from a cheapo airgun)


For a useful number of shots the chamber would have to be at pretty high pressure assuming you're only using the co-ax chamber as an air tank and not feeding through the pilot and dumping the chamber for every shot.
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Unread postAuthor: POLAND_SPUD » Mon Nov 08, 2010 10:12 am

For a useful number of shots
Well actually I've been thinking of an external tank...
though who said you can't add an on board pump?

isn't that one of the harbingers of the apocalypse?

sorry it's not my fault.... 2012 is coming !! :D
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Unread postAuthor: Selador » Mon Nov 08, 2010 10:57 am

Technician1002 wrote:The ball valve can be modified by placing a screw inside the ball at one end and removing the 90 degree stop so it can rotate a full 360. This can make a "cup" of the ball so it will pick up a ball from the top then drop it in with a 180 degree twist. Another 90 degrees will seal the barrel for firing.


OTS: Is that the ballfeild in Toledo ?

The way I would approach the 'cup' idea, would be to find a tap of the appropriate size, and tap one end of the ball.

Then cut a ring, consisting of just a couple of threads width, from an appropriate fitting, and screw/glue that into the ball.

~~~

jackssmirkingrevenge wrote:The problem most people (at least those not conversant with modern binary adhesives Wink) will find is sealing the chamber at the point where the magazine pokes out.


It is difficult, but not impossible, to find a metal washer with an id that is the same as the od of a 3/4" pvc fitting.

Sandwich a metal washer, then a rubber washer, then the chamber wall, then a rubber washer, then a metal washer, on a close nipple, between the tee fitting inside the chamber, and the ball valve outside the chamber.

No glue required, (unless you want to go the extra mile and coat all this with marine goop, between layers.), and it can be disassembled for service.

This -would- require a rather large chamber, though.


BTW: In all your minis, have you ever considered an insulin pen as your basis ?

It has a glass vial in it, that is open on both ends.

Just that one end is sealed with a rubber seal, to allow the insertion of the needle.

And the other end has the rubber plunger.

~~~

POLAND_SPUD wrote:Uhmm that would actually make a pretty cool gun. Since the whole gun is just a long tube


Exactly the reason I am considering a coaxial for my next build.

Yes, yes, I know I am not even finished with my very FIRST build, yet. LOL
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Unread postAuthor: Technician1002 » Mon Nov 08, 2010 12:05 pm

Oxbreath wrote:OTS: Is that the ballfeild in Toledo ?


Nope, Portland Oregon. PGE Park.

A couple of my coaxial launchers resemble a long tube. Neither breech load, but could be modified.
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Unread postAuthor: POLAND_SPUD » Mon Nov 08, 2010 3:16 pm

Yes, yes, I know I am not even finished with my very FIRST build, yet. LOL
Well, no one said that your first build can't be a decent gun, nor that you've got to post 1200 posts here to be good.
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Unread postAuthor: SP00K » Tue Nov 09, 2010 1:42 pm

I'm so glad this topic was brought up. I'm currently working on a coaxial piston pistol and I've been scouring by brain and the internet for ideas on how to breech load it. JSR is totally right, every idea I come up with a seem to run into problems making the mechanism airtight (but it shouldn't be a problem now). I am now considering using a pinball style mechanism to load the projectiles from an external magazine into the barrel. For larger scale cannons with relatively smaller barrels I'm also drawing stuff up on loading ammunition from the piston. PolandSpud's picture is fantastically helpful.
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Unread postAuthor: Selador » Tue Nov 09, 2010 8:34 pm

SP00K wrote:I'm so glad this topic was brought up. I'm currently working on a coaxial piston pistol and I've been scouring by brain and the internet for ideas on how to breech load it. JSR is totally right, every idea I come up with a seem to run into problems making the mechanism airtight (but it shouldn't be a problem now). I am now considering using a pinball style mechanism to load the projectiles from an external magazine into the barrel. For larger scale cannons with relatively smaller barrels I'm also drawing stuff up on loading ammunition from the piston. PolandSpud's picture is fantastically helpful.


I agree. I like Poland-Spud's idea the best.
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 11, 2010 12:20 am

Oxbreath wrote:In all your minis, have you ever considered an insulin pen as your basis ?


Anthing pen-like will fit a small co-axial, and a medical device would be easier to smuggle in places where you shouldn't have a small co-axial, but we don't want to give the wrong people ideas?
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