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expansion barrel for large chamber launchers

Built a combustion cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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expansion barrel for large chamber launchers

Unread postAuthor: sw5amped » Thu Jun 13, 2013 9:55 am

this is actually an attachment I built for my latest build. my launcher has a chamber size of 19.5 inches in length and a volume of around two hundred and fifty cubic inches. having that much volume in the chamber I needed to have a barrel length of almost 10 feet long with the barrel being 1.5 inches in diameter. I have a CB ratio of about .8:1 now.
the reason for my new build was because I kept vaporizing potatoes every time I would fire them out of my gun because my barrel was way too short. my original barrel was about 52 inches long at 1.5 inches in diameter. and now I'm right around 110 inches in length. I built the gun based on a trombone. There is a huge difference in the gun with the new upgrade. Potatoes never exexplode in the barrel and it is much quieter. It still has an awsome kick to it and it can send a spud several hundred yards away!!!!
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Unread postAuthor: Technician1002 » Thu Jun 13, 2013 11:16 am

Interesting concept to reduce the amount of gas that burns out late in the barrel. I've not seen anyone have this problem of spuds that explode in the barrel. What are you using for fuel to have this problem?

Are you using something besides Propane or Mapp gas for fuel?

I have had apples do this, but only ones picked up off the ground that may have rotten cores.

Getting a couple of hundred yards is pretty norm for a good spud gun.
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Unread postAuthor: sw5amped » Sun Jun 16, 2013 6:54 am

I guess I was being modest when I said a few hundred yards. I haven't measured it yet but this gun is amazing!!!! There is a park down the street from my apartment that has three baseball fields and a soccer field. From the parking lot I shoot spuds over everything into the woods that lie beyond the freeway!!. When I shoot my compound rounds or when I have the golf ball barrel on I lose site of those projectiles. I would really like to get this gun chronied. Its gotta be shooting in the 500 fps area. Ill post some more pics. I do have a question though. When I fill my chamber with the mapp, its usually around 40-45 lbs, I keep the chamber ball valve open and run my internal fan for 8 seconds. Then I shut fan off and close the chamber valve then fire. It's perfect everytime. It's that the normal way every gun works?? I heard that when u release the gas into the chamber the chamber should be sealed already? If someone could let me know. Thanks.
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20130613_101601.jpg
Overhead pic of new gun.
20130614_133920.jpg
I have my meter inside pvc . Also the gauge and meter ball valve are in a tight cluster and out of the way. On the end off the clean out cap is my ignition button. The step up transformer is on the other side of the cap or inside the chamber.

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Unread postAuthor: sw5amped » Sun Jun 16, 2013 7:02 am

Here u can see the ignition button. I'm using a12kv step up transformer. Inside the chamber I'm using 2 perforated circuit boards for my multi spark ignition. A board at each end of chamber.
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20130613_101508.jpg
Close up of controls

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Unread postAuthor: jakethebeast » Sun Jun 16, 2013 7:53 am

Tech, mine vaporizes potatoes. Though its 10x hybrid capable of 30x :D
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Unread postAuthor: Labtecpower » Sun Jun 16, 2013 6:00 pm

I can't keep taters in one piece above 2 bar when i'm shooting my QDV :roll:
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Unread postAuthor: sw5amped » Mon Jun 17, 2013 10:59 am

What's a qdv bro?? Also I used the wrong word when I said vaporize earlier. Basically I was blowing the spuds apart before they came out of the barrel. Before this upgrade of course. Now it's perfect. The math on all my formulas came out perfect too. I checked it against latkas calculator. This gun, although a little heavy, is a pleasure to shoot. So much power yet sooooo smooth
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Unread postAuthor: matti » Mon Jun 17, 2013 1:56 pm

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Unread postAuthor: Technician1002 » Mon Jun 17, 2013 2:37 pm

Where are you guys getting soft soggy spuds? Using cooked spuds out of a can can provide those type results.. Fresh spuds work better.
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Unread postAuthor: Labtecpower » Mon Jun 17, 2013 2:55 pm

I'm using Dutch spuds, the best you can get :D
Do canned potatoes even exist? never seen them :roll:
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Unread postAuthor: MrCrowley » Mon Jun 17, 2013 4:19 pm

Technician1002 wrote:Where are you guys getting soft soggy spuds? Using cooked spuds out of a can can provide those type results.. Fresh spuds work better.
Freezing them after cutting them helps a lot too.
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Unread postAuthor: dewey-1 » Mon Jun 17, 2013 4:55 pm

Labtecpower wrote:I'm using Dutch spuds, the best you can get :D
Do canned potatoes even exist? never seen them :roll:


Here you go! :D
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Unread postAuthor: jackssmirkingrevenge » Mon Jun 17, 2013 10:19 pm

Technician1002 wrote:Using cooked spuds out of a can can provide those type results.. Fresh spuds work better.


Just leave then in the can :D

dewey, I can't believe the man from del monte said yes to that :roll:
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Unread postAuthor: sw5amped » Tue Jun 18, 2013 7:36 am

U guys are funny!!!! U don't really shoot canned spuds. Do u?
My spuds were breaking up for 2 reasons. First was my barrel was too short. Second was the spud cutting edge sucked so I was beating the potato down the barrel. Therefore I compromised the integrity of the vegetable!! Not to mention hitting it with a monster blast of mapp didn't help!!! Lol! God I love spud gunning!!
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Unread postAuthor: Technician1002 » Tue Jun 18, 2013 10:11 am

QDV's rock.. Damaged by a t shirt.

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