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Rifled barrels

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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Rifled barrels

Unread postAuthor: us sniper » Thu May 29, 2008 3:09 pm

I was wondering if this idea would work for making homemade barrels. I would cut grooves into a metal or wooden rod, then center it in a larger copper pipe. About 3/4 copper if I wanted a 1/4 barrel. After the smaller rod is centered I would use a backyard foundry to melt aluminum and pour it into the space between the two pipes. Would this workk? Also the casting of the barrel would take a few pour of aluminum because the foundry is not that big.
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Unread postAuthor: SpudFarm » Thu May 29, 2008 3:38 pm

that is just normal casting with an improvised mold.
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Unread postAuthor: STHORNE » Thu May 29, 2008 4:09 pm

sounds like it would work but very time consuming. But if you want to do it, GO 4 IT! :wink:
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Unread postAuthor: us sniper » Thu May 29, 2008 4:38 pm

Do you think that I would be able to twist the rod out after?
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Unread postAuthor: BC Pneumatics » Thu May 29, 2008 4:55 pm

The Al would contract as it cooled, which means the rod should get constricted, and locked in place. I don't know if would be impossible to get it out in once piece, but I am not sure I would rely on being able to use it for another barrel. If it is wood, you could always burn it out. (Then have to clean the barrel) You would also need accurate and consistent twists to be able to back the form out. It also means the Al barrel's OD will be smaller than the copper's ID once cooled. If you plan on leaving the Al in the Cu when you attach it to a launcher, you will likely need to secure it somehow to prevent it from sliding (or getting launched) out of the Cu outer barrel.
All in all, I do not think it is worth the trouble. Though it is a nice example of how as performance increases arithmetically, cost (whether measured in money or effort) increases geometrically.
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Unread postAuthor: STHORNE » Thu May 29, 2008 5:30 pm

BC Pneumatics wrote:The Al would contract as it cooled, which means the rod should get constricted, and locked in place.


Wait. If the aluminum contracted, that would leave the rod loose, and not too hard to get out....or did you just word it wrong?
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Unread postAuthor: BC Pneumatics » Thu May 29, 2008 5:46 pm

Yay, a chance to teach.
Instead of cylinder, lets think of a torus. (A donut shape) As it shrinks, our mind thinks of the diameter of the torus' cross section shrinking, and the inner hole getting larger. (This would be the wall of our hollow cylinder getting thinner.) What we do not think about is the (average) circumference of the torus. A circumference is just a line bent around into a circle. As the Al shrinks, this line contracts, getting shorter. Thus the circumference shrinks, and the inner hole is smaller, locking the rod in place.
What I failed to mention earlier, that is bound to be a more significant effect, is the shrinkage along the length of the barrel. This is going to lock the form up very tight.
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Last edited by BC Pneumatics on Fri May 30, 2008 1:14 pm, edited 1 time in total.
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Unread postAuthor: Tooo Easssyy » Fri May 30, 2008 4:57 am

Yeah should work, give us a yell if it does i really wanna make a golf ball sniper
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Unread postAuthor: jimmy101 » Fri May 30, 2008 1:06 pm

BC Pneumatics wrote:Yay, a chance to teach.
Instead of cylinder, lets think of a torus. (A donut shape) As it shrinks, our mind things of the diameter of the torus' cross section shrinking, and the inner hole getting larger. (This would be the wall of our hollow cylinder getting thinner.) What we do not think about is the (average) circumference of the torus. A circumference is just a line bent around into a circle. As the Al shrinks, this line contracts, getting shorter. Thus the circumference shrinks, and the inner hole is smaller, locking the rod in place.
What I failed to mention earlier, that is bound to be a more significant effect, is the shrinkage along the length of the barrel. This is going to lock the form of very tight.

Kind of a long explanation!

Short and sweet:
A hole in a piece of material expands/contracts with changes in temperature exactly as if the hole was filled.
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Unread postAuthor: BC Pneumatics » Fri May 30, 2008 1:16 pm

I have never thought of it in that way jimmy. You are right, it is much a shorter and simpler way of looking at things.
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