SpudFiles

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)

I would recommend starting here;

http://www.spudfiles.com/spud_wiki/inde ... esign_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.

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.

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.

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