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construction materials

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Unread postAuthor: roygaddis » Tue Feb 26, 2008 11:20 am

Not that anyone asked,but in my humble opinion the best expansion chamber is made from a large,(say 20 lb) fire extinguisher tank.The best barrel is made from a piece of 1" copper pipe about 4' long.The best propellant is oxygen and butane,and the best projectile is the bottom end of a ski pole wrapped with cord and topped with shrink tube.You won't blow it up,the smaller barrel concentrates more force,the propellant burns completely and the projectile will penetrate just about anything.Even rock.I've fired through both car doors and into a 55 gallon drum on half a balloonful of oxygen and two tiny shots of butane.C batteries work pretty good,too.Or you can use a 11/4" barrel and use those cheap,driving range golf balls -with the shell taken off- as projectilesThey will bounce back after going through a cinderblock and two bricks,though,so shoot from behind protective cover.
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Unread postAuthor: brogdenlaxmiddie » Tue Feb 26, 2008 11:26 am

Why exactly was this needed or helpful?


BTW- Welcome to the forum 8)
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Unread postAuthor: jackssmirkingrevenge » Tue Feb 26, 2008 11:33 am

Nothing better than a few photos and/or videos to back up your humble opinion and lend more weight to your argument ;)
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Unread postAuthor: MrCrowley » Tue Feb 26, 2008 10:15 pm

Ah thanks for that... You have a lot to experiment with, try pneumatics.
Then your humble opinion might change :wink:
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Unread postAuthor: Eddbot » Wed Feb 27, 2008 1:20 am

Wait...i don't get it. What does this accomplish? Oh, and what ^ said, yeah...
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Unread postAuthor: Carlman » Wed Feb 27, 2008 1:23 am

Eddbot wrote:Wait...i don't get it. What does this accomplish?


thats the point eddbot
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Unread postAuthor: DYI » Wed Feb 27, 2008 5:41 pm

You have much to learn, young grasshopper :wink:

Welcome to the forum. If you have this launcher of yours, post it in whichever showcase is appropriate.
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Unread postAuthor: SpudBlaster15 » Wed Feb 27, 2008 8:47 pm

the smaller barrel concentrates more force


Sorry for being the Physics Nazi, but that is a misconception too many people seem to have. Given equal chamber pressures, a barrel with a larger diameter will allow for the application of more force to the projectile than will a smaller diameter barrel. Force is pressure multiplied by area, and a larger diameter naturally implies greater area. To be specific, Force on the projectile will be directly proportional to the barrel diameter squared.
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Unread postAuthor: jr » Wed Feb 27, 2008 8:57 pm

Yes the 20# fire extingisher is the correct chamber but I use mine to build a pneumatic....it is allmost finished. I am going to epoxy the fitting to the chamber just for good measure.

have it posted in a day or so..
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Unread postAuthor: DYI » Wed Feb 27, 2008 9:31 pm

While we're on that topic, O<sub>2</sub>/MAPP is better than O<sub>2</sub>/C<sub>4</sub>H<sub>10</sub>, ski poles aren't very good ammo at all, and I really doubt that such a small launcher running on atmospheric pressure O<sub>2</sub>/C<sub>4</sub>H<sub>10</sub> could put a projectile like a golfball through a cinderblock and 2 bricks without some very odd circumstances in play.

Once again, seeing is quite a bit closer to believing than is reading, so we want videos, or at least pictures.
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Unread postAuthor: jackssmirkingrevenge » Wed Feb 27, 2008 11:44 pm

SpudBlaster15 wrote:Sorry for being the Physics Nazi, but that is a misconception too many people seem to have.


The're probably thinking of firearms, this is the general idea behind the taper or squeeze bore gun as used by the Germans in their sPzB 41 anti-tank gun.

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Unread postAuthor: Ragnarok » Thu Feb 28, 2008 8:47 am

jackssmirkingrevenge wrote:They're probably thinking of firearms

No, a lot of people I know have thought the same thing, and they're hardly firearms savvy.

People just imagine that force from pressure can just be concentrated down, thinking that the imaginary "lines of force" will the air flow path - which isn't the case.
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Unread postAuthor: Jared Haehnel » Thu Feb 28, 2008 9:57 am

You need more details... Is it pure O2 and butane? Is it at atmoshperic pressure or is it a pressurized? Do you have pictures? Can you take pictures...


Honestly I just can't see a golf ball going through concret bricks, the out side shell is the hardest part of the ball..if you remove that you just have giant boucy ball...

And Ragnarok is right... the pressure isn't concetrated just becuase the object is smaller... the only advantage you have over using a small barrel is you generaly have lighter ammo and greater vilocitiescompared to a larger bore... but that doesn't include sabots
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Unread postAuthor: jackssmirkingrevenge » Thu Feb 28, 2008 10:08 am

Jared Haehnel wrote:Honestly I just can't see a golf ball going through concrete bricks


I can :D
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Unread postAuthor: Jared Haehnel » Thu Feb 28, 2008 10:13 am

Jared Haehnel wrote:
Honestly I just can't see a golf ball going through concrete bricks


I can


I ment with the design he had presented...the velocity would not likely be high enough...
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