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best barrel length

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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best barrel length

Unread postAuthor: shud_b_rite » Mon Feb 05, 2007 3:06 am

Using ggdt I figured out that for my cannon the best barrel length for achieving maximum speed (m/s) is about 200cm. At the moment my barrel is about 70cm with 1.5cm diameter. I can understand why having a longer barrel accelerates a projectile faster than having a short barrel but can someone please explain to me why having a barrel that is too long can slow down or reduce the top speed of the projectile?
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Last edited by shud_b_rite on Mon Feb 05, 2007 3:18 am, edited 1 time in total.
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Unread postAuthor: experament-u2 » Mon Feb 05, 2007 3:10 am

i think it might just run out of gas and then theres friction

i truly dont know but that might be able ti help
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Unread postAuthor: Insomniac » Mon Feb 05, 2007 3:48 am

If the barrel is too long, 2 things will happen.

1. There will be no gas pushing the projectile foward, and it will be slowed down from friction with the barrel.
2. The projectile will act as a piston and generate a vaccuum behind it, slowing it down even more.

Hope that helps.
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Unread postAuthor: Recruit » Mon Feb 05, 2007 4:31 am

What insomniac said. In a pneumatic the friction from the barrel would slow it down after so long because the expanding gas after so far equalizes with the outside preassure. and if you have a projectile that seal in the barrel well then is will be gin forming a vaccum behind it.
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