SpudFiles

ive noticed that when i put the barrel of a mini cannon and fired it, a large amount of water got sucked into the chamber so the same must be happening in large ones (not in water) so it might be a good idea to put on-way valves on the chamber some air can be sucked into the chamber thus inproving shooting distance. its just a thaught.

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b/c it might still occur, when the explotion pushs out the potato the outside air would want to replace the air that got burned up from the combustion.

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yea no real need. just get a chamber fan. Glad your thinking though!

I think he meant to use the pressure difference to further propel the projectile.
In an "ideal" cannon, the pressure behind the projectile would be equal to the one in front of it (atmospheric pressure) when it passes the muzzle.
In real life (spudguns and weapons in general), there's quite a bit of pressure left behind the projectile by the time it leaves the barrel. Due to inertia, the leftover gas propels the projectile for a split second even after it exits the barrel.
By the time the gas would be cool enough to create a vacuum, the projectile would have been long gone.

And, for the record, what happens in water is quite different to what happens in air, as far as our little part of ballistics is concerned.

kris wrote:b/c it might still occur, when the explotion pushs out the potato the outside air would want to replace the air that got burned up from the combustion.

god idea glad ur thinkin but really the diffrnce to make a sucsessful one of these that improved distace would only be a foot mabey? the explosion s rapid expansion wich is filling the space of the cannon. the air along with the fuel turns into a plasma (one physical state up from "gas" [like air] in which the molecuels of the element/substance are ionized) any suction which could even potentially cause an effect on the spud acurs after it is lauched clear from the barrel. plus any opening alos the explosions pressure to escape faster another way.

compressed air to fill it make sure that there is in suction would then just be a hybrid.

~Z.S.~

If your idea is to relieve the suction created during launch... you don't have to worry about that; most barrrels arn't long enough to notice the effect.

Furthermore, if you did have that problem, it'd be simpler to just shorten the barrel.