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Pepsi round vs 3/4" barrel.

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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Pepsi round vs 3/4" barrel.

Unread postAuthor: boyntonstu » Sun Feb 21, 2010 7:06 pm

Force = mass x acceleration

Acceleration = Force/mass

Pressure = Force/Area

Force = Pressure x Area

Given these 2 fundamental laws of Physics what would make a powerful cannon?

A LARGE bore barrel.

A Pepsi can is about 2.6" in diameter and has an area of 5.3 square inches.

3/4" L copper ID is 0.785" and has an area of 0.438 square inches.

The ratio of areas is 5.3/.438 is 12.1:1

If your chamber is pressurized to 100 psi the projectile in a 3/4" barrel will have 43.8 pounds of force pushing on it when you pull the trigger.

If your barrel was 2.6" in diameter, the soda can will have 530 pounds of force pushing on it when you pull the trigger with the same 100 psi..

The question of practicality comes when it comes to size, weight, volume of the chamber, the time it takes to pressurize it, etc.

Boiling it down to a few simple numbers, a 3/4" barrel requires 200 psi to generate 100 pounds of force.

The same 100 psi will impart 1,060 pounds of force to a Pepsi can.

Just thinking out loud.
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Unread postAuthor: Demon » Sun Feb 21, 2010 7:29 pm

This is exactly what i was thinking a few hours ago.

A 40mm barrel at 160 psi firing a 10mm ball bearing sabot would be pretty powerfull (thats 200 foot per lbs)

Maybe enough to get some decent accuracy at "long ranges"
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Unread postAuthor: deathbyDWV » Sun Feb 21, 2010 9:19 pm

Yay!!! I like maths. That is the main reason I build large bore cannons. Without access to high pressure... Moar powar for less pressure!
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Unread postAuthor: jackssmirkingrevenge » Mon Feb 22, 2010 1:22 am

This basic principle is exactly why discarding sabot projectiles work so well.

One thing you have to consider though is that a bigger barrel needs a bigger valve. A 3/4" piston valve might give you say 100 psi in a 3/4" barrel, but in a 2.5" barrel the air has more space to expand so it will lose pressure.
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