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pneumatic barrel to chamber

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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pneumatic barrel to chamber

Unread postAuthor: kydavies » Mon May 10, 2010 6:29 pm

i am building a pneumatic bazooka that shoots squash balls, i need to know what barrel to chamber length to use ( both chamber and barrel ar 1.5" PVC and the over all length of pip i have is 36 inches)
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mikemurph wrote:yea, the ammo has been changed to a more aero dynamic projectile. it consists of the back half of a dart, and a hot glue ball
AHahahahah!!
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Unread postAuthor: Technician1002 » Mon May 10, 2010 7:12 pm

I would recommend starting here;

http://www.spudfiles.com/spud_wiki/index.php?title=Gas_Gun_Design_Tool

The dimensions you need will vary depending on pressure used and projectile mass. You can model your designs with this software and decide what is best for you.
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Unread postAuthor: btrettel » Mon May 10, 2010 7:58 pm

The optimal C:B ratio depends on the pressure used when the projectile mass is above a certain critical mass that depends on a number of factors. If your projectile is pretty heavy, this is probably true.

<table border="1"><tr><td>P_c*</td><td>C:B</td><td>efficiency</td></tr><tr><td>1.75</td><td>2.54352</td><td>0.17151</td></tr><tr><td>2</td><td>1.87803</td><td>0.22151</td></tr><tr><td>2.5</td><td>1.25462</td><td>0.29807</td></tr><tr><td>3</td><td>0.95535</td><td>0.35443</td></tr><tr><td>3.5</td><td>0.77841</td><td>0.39807</td></tr><tr><td>4</td><td>0.66092</td><td>0.43314</td></tr><tr><td>5</td><td>0.51371</td><td>0.48655</td></tr><tr><td>6</td><td>0.42449</td><td>0.52582</td></tr><tr><td>7</td><td>0.36424</td><td>0.55625</td></tr><tr><td>8</td><td>0.32058</td><td>0.58073</td></tr><tr><td>9</td><td>0.28740</td><td>0.60098</td></tr><tr><td>10</td><td>0.26121</td><td>0.61808</td></tr><tr><td>12</td><td>0.22239</td><td>0.64558</td></tr><tr><td>14</td><td>0.19482</td><td>0.66690</td></tr><tr><td>16</td><td>0.17417</td><td>0.68404</td></tr><tr><td>18</td><td>0.15805</td><td>0.69820</td></tr><tr><td>20</td><td>0.14503</td><td>0.71014</td></tr></table>

See this thread for more information: http://www.spudfiles.com/forums/optimal ... 20850.html

GGDT is good, but it doesn't tell you how to design. These rules do. Use both and do some testing with a chronometer too. :wink:
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Last edited by btrettel on Tue May 11, 2010 7:52 am, edited 1 time in total.
All spud gun related projects are currently on hold.

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Unread postAuthor: kydavies » Mon May 10, 2010 11:55 pm

sweet thanks i got impatcient and cut my pipe so i have a 20 inch barrel and a 14 inch chamber,still waiting for my sprinkler valve to come in and the im goingto mod it for pneumatic opperation and finish my alder stock, foregrip and trigger system s il be done in about a week.
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mikemurph wrote:yea, the ammo has been changed to a more aero dynamic projectile. it consists of the back half of a dart, and a hot glue ball
AHahahahah!!
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Unread postAuthor: MRR » Tue May 11, 2010 10:34 am

I don't think that squash balls make good ammunition. They offer way too much friction and will deform inside of the barrel.
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