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co-axil piston gun help

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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co-axil piston gun help

Unread postAuthor: itsnotmyblood » Fri Jun 18, 2010 3:24 pm

so im making my first pneumatic cannon. its going to be a co-axil piston gun. i want to use a 2inch chamber and a 1inch barrle. i dont know if there is a high enuf chaber to barrle ratio for good performance. just want to know if it will work
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Unread postAuthor: Ranger » Fri Jun 18, 2010 3:28 pm

That should be good. I ran the numbers with a 36" barrel and 32" chamber and came out with a about 2:1.
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Unread postAuthor: clemsonguy1125 » Fri Jun 18, 2010 3:31 pm

Thats what tech did on his mouse musket
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Unread postAuthor: Lockednloaded » Fri Jun 18, 2010 3:48 pm

Ranger wrote:That should be good. I ran the numbers with a 36" barrel and 32" chamber and came out with a about 2:1.

Ahh, but you forget to subtract the volume of the barrel inside the chamber from the volume of the chamber, so you probably get a ratio closer to 1:1
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Unread postAuthor: itsnotmyblood » Fri Jun 18, 2010 3:49 pm

that makes more sense
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Unread postAuthor: itsnotmyblood » Fri Jun 18, 2010 3:58 pm

im trying to use ggdt it keeps telling me the barrle is exesivly long when its shorter than the chamber?
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Unread postAuthor: Lockednloaded » Fri Jun 18, 2010 4:17 pm

what numbers are ou plugging in, take a screenshot because it sounds like a user error
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Unread postAuthor: itsnotmyblood » Fri Jun 18, 2010 4:25 pm

how do i take a screen shot? i dont know what alot of these numbers are for? whats a seat? how do i know the friction on the projectile?
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Unread postAuthor: Ranger » Fri Jun 18, 2010 4:58 pm

Lockednloaded wrote:
Ranger wrote:That should be good. I ran the numbers with a 36" barrel and 32" chamber and came out with a about 2:1.

Ahh, but you forget to subtract the volume of the barrel inside the chamber from the volume of the chamber, so you probably get a ratio closer to 1:1


I hope my math is right

Barrel: 1"x36" = 28 cubic inches
Chamber: 2"x32"= 100 cubic inches
OD of barrel: 1.25x32=39 cubic inches

100-39=61

61/28= 2.17

"About 2:1" :D
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Unread postAuthor: itsnotmyblood » Fri Jun 18, 2010 5:02 pm

i want the chamber 60" the barle 56.5"
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Unread postAuthor: itsnotmyblood » Fri Jun 18, 2010 5:06 pm

how dose 1 times 36 get 28
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Unread postAuthor: Ranger » Fri Jun 18, 2010 5:26 pm

Its a cylinder volume equation

Formula for finding the volume of a cylinder : pi * radius2 * height

I go Here and it makes it much eaiser

How can you make the barrel shorter than the chamber? They either have to be the same length or the barrel has to be longer. Think about it.
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Unread postAuthor: Technician1002 » Fri Jun 18, 2010 5:44 pm

Ranger wrote: How can you make the barrel shorter than the chamber? They either have to be the same length or the barrel has to be longer. Think about it.


This barrel is most certainly shorter than the chamber. It is only longer when I screw on an extension.
[/img]
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PistonClearance.jpg
Chamber is over a foot long. This barrel is threaded on the end for extensions. It is 2 inches long. This is a coaxial.
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Unread postAuthor: Ranger » Fri Jun 18, 2010 6:32 pm

*If* we are talking about coaxials designed on the principles Here (the third animation) Then the chamber (the one that supplies air to the barrel, not the pilot area) cannot be longer than the barrel. In a *standard* coaxial, the barrel cannot be shorter than the chamber.

Technician, we are talking about coaxial piston valve cannons not your awesome QDV design.
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Unread postAuthor: Technician1002 » Fri Jun 18, 2010 6:44 pm

itsnotmyblood wrote:how do i take a screen shot?


In Widows, Press PrintScreen. Then open paint or other image editor and select Paste to put your capture in the program. Edit and resize as needed, then save.

In Ubuntu, use the Applications pull down and under Accessories, select Screenshot. Give the capture a name or use the default.

Open the image in your favorite image editor to crop, resize, or modify and save the changes.

On a Mac, I don't know. I don't use one.

Technician, we are talking about coaxial piston valve cannons not your awesome QDV design.

By definition, that is a coaxial as the chamber and barrel are on the same axis.

In my golf ball bazooka the barrel is shorter than the chamber. The breech of the barrel does not reach the breech of the chamber. The muzzle is recessed and ends very shortly past the end of the chamber. It isn't much shorter, but it is shorter.
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ScreenCap.jpg
Screen capture of this page.
Muzzle.jpg
Muzzle of the GB coaxial.
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