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Straight barrel vs. bent 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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Straight barrel vs. bent barrels

Unread postAuthor: tvouthilak » Fri Nov 14, 2008 10:46 am

I'm working on a new spud cannon design and was wondering something. Is there any disadvantage of putting bends in your barrel vs. a straight barrel? I'm planing on putting a couple 90 degree bends in my barrel and was wondering if this would decrease its performance.

the barrel will look like this
......___________
___|
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Unread postAuthor: CpTn_lAw » Fri Nov 14, 2008 10:59 am

Lol, if you plan on shooting the projectile through the two 90 ° (which i wish you good luck with) , you'll end up with two unuseable elbows. If in the contrary you just wanna do this for a design matter, it will work, but it will add dead space between the valve and the projectile. This is not bad in itself, but it will decrease the performance.
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Unread postAuthor: starman » Fri Nov 14, 2008 11:00 am

Bends in your barrel or in your chamber? Your little drawing there is useless.

The over and under design is common and uses some 90 bends out of the chamber to the valve or piston, which then powers a straight barrel.
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 14, 2008 11:01 am

Not going to work, the projectile will just slam through the first elbow. At best you can get away with a gentle curve, like the krummlauf:

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Unread postAuthor: PVC Arsenal 17 » Fri Nov 14, 2008 2:57 pm

I think he's talking about introducing air into the barrel through elbows, not firing the actual projectile through the elbows. I may be wrong.

But if you plan on shooting a projectile through elbows, forget it.

If you plan on redirecting air using elbows, it will work but with reduced power.
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Unread postAuthor: tvouthilak » Fri Nov 14, 2008 9:50 pm

CpTn_lAw wrote:If in the contrary you just wanna do this for a design matter, it will work, but it will add dead space between the valve and the projectile. This is not bad in itself, but it will decrease the performance.


yeah, you hit the nail on the head. So the dead space between the valve and projectile is the main issue. Are we talking about a significant decrease in performance or something that would hardly be noticeable by the naked eye? So lets say a straight barrel is 100% efficient, then what would you say a barrel with 2 90 degree elbows in it be (85-90%) ????

Thanks for all the responses guys.
BTW, I may be a noob to all this, but even I know you can't shoot a projectile through a 90 degree bend. :roll:
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Unread postAuthor: Insomniac » Fri Nov 14, 2008 11:10 pm

Both the dead space and the way the air has to redirect itself twice will reduce performance a little, but it shouldn't be too bad.

The reason people got confused was because you kept calling the whole thing, elbows included, the barrel. Generally we think of the barrel as the part the projectile actually travels through, and any other piping attached between it and the valve is just additional piping.
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Unread postAuthor: tvouthilak » Sat Nov 15, 2008 12:17 am

Insomniac wrote:
The reason people got confused was because you kept calling the whole thing, elbows included, the barrel. Generally we think of the barrel as the part the projectile actually travels through, and any other piping attached between it and the valve is just additional piping.


Thanks for your response. You make a good point. sorry for any confusion I may have caused. I'll try to be more clear on future posts. Like I said, I'm new to this stuff so I'm still getting used to the terminology. :?
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Unread postAuthor: Insomniac » Sat Nov 15, 2008 3:07 am

tvouthilak wrote:Thanks for your response. You make a good point. sorry for any confusion I may have caused. I'll try to be more clear on future posts. Like I said, I'm new to this stuff so I'm still getting used to the terminology. :?


Meh, don't worry about it. You are already in our good books by actually taking enough time to spell and punctuate your posts. It gets so damn annoying when people try and ask a question in text talk, and you have no idea what they were trying to say. BTW, if you want to post a diagram or somthing it is more effective to just draw up a rough sketch of it in paint and upload it.
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Unread postAuthor: Hydra » Sat Nov 15, 2008 3:23 am

Lots of people do it actually
Check out the SpudWIki, search "Pneumatic Spudgun" and theres a picture of an over-under pneumatic.

Some people here think that noobs are really dumb...like, they have no common sense at all. Knowing if you can shoot something through 2 90 degree bends doesnt need you to know alot about guns, its just common sense.
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Unread postAuthor: tvouthilak » Sat Nov 15, 2008 9:48 pm

Here's a quick sketch of my design. The top picture is the overall concept. You can see in the blow up the valve is at the bottom. When the piston opens, the air travels through the pipe taking a 90 turn up and then through the 'T' which is plugged at the back to direct the air forward where the projectile will be waiting. The bottom picture is my original design which you can see here

The new design is basically my original turned upside down, thus the need to redirect the barrel to bring it back up to the top. The only reason for this change is to bring the solid part of the chamber to the top so I have a place to rest my cheek when the gun is at my shoulder. Before, I would have to place my cheek on the sprinkler valve and when it opened, the air coming out would be right at my ear which is very loud.

The rail you see under the barrel will be used as a guide for my pump action reload I am working on.

Any comments or suggestions on the new design would be greatly welcomed.
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Unread postAuthor: psycix » Sun Nov 16, 2008 6:33 pm

Too bad. I'd always wanted so see a gun that shot a GB through 2 elbows as barrel. :D

About your design:
There COULD be flow restriction if your valve porting and "dead space" is less in diameter then your barrel.
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Unread postAuthor: judgment_arms » Mon Nov 17, 2008 10:59 am

looks okay by me...

dead space is not as bad a thing as most people make it out to be, a lot of old powder burner howitzers had an air chamber behind the powder area to allow the gasses a place to expand a bit before acting on the projectile, which allowed for a full force hit rather than a push.

and while air cannon and their powder burning brothers have little internal ballistics in common, I've had problems with my zero dead space cannon shredding projectiles rather than shooting them.



what's the projectile this cannon is being designed to shoot, or did I miss that?
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Unread postAuthor: tvouthilak » Mon Nov 17, 2008 9:22 pm

judgment_arms wrote:looks okay by me...

what's the projectile this cannon is being designed to shoot, or did I miss that?


No you didn't miss it. My plan is to shoot marbles with it. Using a 1" barrel for large marbles and a 1/2" barrel insert for smaller marbles. So there should be no fear of shredding the projectile as you had mentioned. :lol:
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Unread postAuthor: judgment_arms » Tue Nov 18, 2008 9:22 am

tvouthilak wrote:
judgment_arms wrote:looks okay by me...

what's the projectile this cannon is being designed to shoot, or did I miss that?


No you didn't miss it. My plan is to shoot marbles with it. Using a 1" barrel for large marbles and a 1/2" barrel insert for smaller marbles. So there should be no fear of shredding the projectile as you had mentioned. :lol:


no, I guess not! :D
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