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Carrot Gun

Built a pneumatic 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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Carrot Gun

Unread postAuthor: PCGUY » Sat Feb 05, 2005 12:01 am

<div align="center">Carrot Gun

Provided By - Pacogoatboy

This is a very simple design for a carrot gun. I built it recently in one day, spending only $15 using a few parts I already had in my garage. With no supplies at all, it might be as much as $25. It is not a gun for distance, but it does make a nice pop and can do some very serious damage at close range. Please be careful with this, I've broken 1/2 inch thick cedar boards using frozen candy as ammo, and I would hate to think what it might do to something living. Longer distance shots can be erratic due to the light weight of the ammo, so make sure you have a clear field of fire. You might want to modify this with an extra pair of tees connecting the chamber and the barrel more directly so that the air doesn't have to follow as convoluted a path toward the barrel as it does in this design.

Drill (3/8" bit)
Saw (a miter saw works well, but any saw capable of making clean cuts on short lengths of pipe is acceptable)
Crescent Wrench or Pliers
Flat Headed Screwdriver

The parts are color coded in the diagram as follows: (All prices are approximately what I paid at Lowe's)
6 x Red = 1/2" sch 40 PVC 45 degree elbow ($0.25)
2 x Dark Green = 1/2" x 1" sch 40 PVC 90 degree reducing elbow ($0.75)
1 x Light Green = 20 oz. plastic pop bottle (Free. A 2 liter would work also. You need the small cap size for this design. Use a good bottle that is not damaged in any way shape or form.)
1 x Pink = 1" sch 40 PVC plug ($0.25)
3 x Purple = 1/2" sch 40 PVC pipe ($1 for 5')
2 x Dark Blue = 1/2" sch 40 PVC male adapter ($0.17)
2 x Blue = 1/2" sch 40 PVC 90 degree elbow ($0.25)
1 x Light Blue = 1/2" sch 40 PVC tee ($1)
Orange = bronze fittings (a 1/2" threaded ball valve = $5 and a brass Schrader valve = $5)
Required but not shown:
PVC primer (yes, you MUST use primer) ($2)
PVC cement ($2)
JB Weld (or other strong, pressure resistant epoxy) ($4)
Teflon Tape ($1)
One narrow screw. As thin as possible and between 1/2" and 3/4" in length. A thin nail and some epoxy would work as well. (Free, or awfully close to it.)
Small hose clamps as needed for stability (also could use duct tape) ($5)


Note: Each of the fittings shown touching another is connected to it by a 1/2"x1.5" piece of pipe. At this length, they should butt up against each other perfectly with the PVC inserted completely. I would assemble in the order listed below, though it really won't matter too much if you are careful. As with any PVC welds, you MUST let them cure for a day to ensure that they do not leak. It is difficult to fix leaky fixtures, and it is much more worth your time and money to just wait a little bit before shooting. Using good solvent welding techniques allows you to create spud guns reliably without leaks.

Chamber Fitting Assembly

Mix a sizeable amount of JB Weld epoxy on a scrap of cardboard or other disposable surface. Do not wait for it to stiffen before using.

Lightly scratch the 1" opening of one of the 1/2"x1" elbows with a screwdriver or razor knife so that the epoxy will be able to stick to it.

Drill a hole through the top of the pop bottle cap, leaving the blue rubbery gasket inside of it intact around the edges. Leave at least 1/8" of plastic around the edges of the cap. If you damage the gasket, get another cap and try again.

Using your little finger, smear as thick a layer as possible of JB Weld on the inside of the 1" opening of the elbow, going in as deep as the height of the cap (about 1/2").

Slide the cap into the 1" opening, making sure that there is enough JB Weld to fill all the way around, but that it is not filling the hole you drilled in the top of it. Also make sure that there is no epoxy on the threads of the cap.

Place a piece of duct tape sticky side up in a flat surface that will not be disturbed for the next six hours and press the epoxy filled end of the elbow against it, sealing it off.

Stick a finger into the other end of the elbow and press the cap down against the tape as well.

After about 6 hours (more if it is cold), peel off the tape carefully and inspect the epoxy. It should have filled in the space between the cap and the PVC completely, leaving no air gaps. If any epoxy has gotten onto the threads of the cap, scrape it off with your fingernail or cut it away with a razor knife. If it has not filled the gap between the cap and the walls of the fitting, try to fill in the hole from the top and the bottom of the fitting.

Though you can cement this fitting to the rest of the gun at this point, do not pressurize this fitting until the epoxy has cured completely, which takes at least 12 hours.

Stock Assembly

Cement the parts for the stock of the gun together as shown, starting from the 45 degree fitting below the valve and working back toward the chamber.

Assemble the pieces on a flat surface so that you can keep everything lined up nicely. Most PVC fittings have marks from the molds used to make them. These small lines are a good way to keep everything straight. If you don't keep the stock straight, it will not only look bad, but it will be less comfortable to hold and shoot.

Guess a comfortable length for the top flat part of the stock and connect it. (I used about 9.5" of PVC, for an 8" extension. The other 1.5" was used to connect the fittings at either end.)
The shoulder butt is made from a piece of PVC that is about 5-6" long, with 1.5" used to connect the fittings.

Measure the distance from the top right of the stock to the first 45 degree fitting used. Use this length as the length of the bottom of the stock.

Connect the tee as shown, but without the plug.

Assuming it has hardened, cement the epoxy filled fitting onto the end of the stock.

Drill a 3/8" hole through the top of the 1" plug.

Insert the Schrader valve through the hole and feed it into the chuck of your drill.

With the drill in reverse, slowly thread the Schrader valve through the fitting.

Most of the threads of the valve will not come through. It is better to not distort the rubber gasket at the valve's base too much or you might end up with leaks. Screw the washer and nut onto the valve tightly and cement the fixture onto the stock.

Valve and Barrel Assembly

Wrap the male adapters securely with 6 or 7 wraps of Teflon tape.

Screw them into either side of your valve tightly.

Cement the valve onto the stock, making sure that it is oriented in a comfortable way for you. I personally have the valve so that opening it requires a backward pull with my thumb above the stock, much like cocking a pistol.

Cement a 45 degree elbow onto the end of the barrel (a 5' piece of 1/2" PVC in my case).

Drill a small pilot hole through the top part of the 45 degree elbow that contains the 1/2" PVC and screw your screw into that hole. This will keep small ammo from rolling back into the fitting, decreasing the gun's power.

Cement the barrel onto the other male adapter of the valve, making sure that it is aligned with the stock of the gun. Hold it in place for a minute or so to ensure that it dries in the correct alignment.

Barrel Stabilization

Because PVC is flexible in thinner diameters, I've done the following to stabilize my barrel.

Cut a piece of PVC so that it is 3" shorter than your barrel.

Primer and cement this PVC along the entire length of one face. (It doesn't matter if the cement dries before you attach it. It is just there for added friction.)

Primer and cement the top face of the barrel.

Place the two cemented faces together and clamp them with a hose clamp near the base of the barrel.

Place another hose clamp about 15" further down the barrel, trying to keep them lined up with one another.

Place a third and fourth hose clamp, loosely fitted, at 15" increments down the barrel.

Sight through the open pipe to see whether it is bending in any particular direction. If it is, loosen the hose clamps, bend the pipe the other way at that location, and tighten them again.

Do this until both pipes are not deflected vertically or horizontally. The PVC cement should help you make an adjustment and keep it in the new position until you are able to tighten the hose clamps.

Near the bend before the barrel, you may wish to attach one more larger hose clamp to connect the chamber area to the barrel area for greater stability. Use a spacer if these two areas are not already in very close proximity (less than an inch apart.)

Loading and Firing

Open the trigger valve.

Using a projectile that is about the same size as the barrel, load the gun from the barrel end. You may need a ramrod to push the projectile back against the stop. I use 1.5' metal rods that I happened to have lying in my garage. Collapsible tent posts might work well too.
Close the trigger valve.

For the first shots, wear earplugs and safety glasses. It would not hurt to do this for all shots, but most people won't do it.

Pressurize the chamber using a bicycle pump or a regulated compressor. For the first shot, pressurize slowly, listening along the length of the gun for leaks. If a leak is detected, locate it precisely by squirting soapy water onto the fitting and watching for bubbles. Leaks can be fixed with epoxy. After about 60 psi, you should no longer need to worry about leaks and should use your earplugs.

I pressurize my chamber to 140 psi, which takes about 35 pumps. The bottle will become hot and incredibly rigid. Don't do anything stupid like trying to make a dent in it or pop it though, because the bottle could explode, sending slices of plastic into whatever surrounds it.
Point the gun in a safe direction and open the valve to fire.


Provided By - Pacogoatboy</div>
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Unread postAuthor: spoink » Thu Apr 20, 2006 1:11 pm

i made one of those but i used a 3" pipe to make the air tank
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Unread postAuthor: Z0Z0 » Mon Aug 14, 2006 12:58 pm

you probably lose quite a bit of power running it through the stock...
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Unread postAuthor: SpudStuff » Mon Aug 14, 2006 1:03 pm

dead topic
dead topic
dead topic
dead topic
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Unread postAuthor: Steve- » Mon Aug 14, 2006 1:11 pm

your allowed to post on dead topics in the official cannon section
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Unread postAuthor: PVC Arsenal 17 » Mon Aug 14, 2006 9:57 pm

Steve- wrote:your allowed to post on dead topics in the official cannon section

which is no more...
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Unread postAuthor: abcdefg » Fri Jan 12, 2007 6:25 pm

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Unread postAuthor: akaddis » Tue Jan 16, 2007 2:56 pm

lol...carrot gun!!!
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