How to make a spud gun with Sureshot SIK-20

A place for general potato gun questions and discussions.
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Tue Aug 18, 2009 10:06 pm


WITH SURESHOT KIT (<a href=" ... >SIK-20</a>)

AVAILABLE FROM <a href="">www.ul ...</a>

SIK-20 Standard Igniter Instructions

These instructions are intended to help you build an effective yet simple spudgun.

1. These instructions/procedures are provided as-is. No guarantee is made that this device will function as well or better as I have experienced, intend, or describe it to operate. In other words, your results may vary, and they may even be very undesirable results, possibly resulting in personal injury or property damage. Please review the site disclaimer for more information.

2. The wording and statements/nomenclature pertaining to the construction and operation of this potato launcher are intended as such to help ensure one attempting to do this has a basic understanding of the equipment and materials involved. If some of the statements seem 'Greek' to you or you do not recognize some symbols or phrases, that is wholly my intent, and you should obtain assistance from a trusted source or not proceed at all.

3. These instructions are intended for a beginner or someone that has never built a spudgun before. The procedure outlined below is not necessarily the method myself or another experienced spudgun builder uses. These instructions will help guide you in building a "sound" piece of launching hardware. As you gain experience, you may find that different things may work better for you.... but start simple. Thanks, and happy spudding!

Keep in mind that PVC pipe/fittings are not approved by the manufacturer to be used for the purpose of constructing spudguns.

Step 1: Getting stuff to build it

This materials list is to build a very simple starter model potato launcher, with the intent to get the most bang from your buck (so to speak). By no means is this the only way to build a launcher, or nearly the coolest, but still able to provide hours of fun. Also, make sure to obtain pressure rated parts for building your spudgun. We do not recommend ABS or cellular core type pipe and fittings, these are not pressure rated and unsafe.


Obtain the following items:

1. 12" of 4" SCH40 PVC Pressure Rated water pipe (chamber body)

2. 48" of 2" SCH40 PVC Pressure Rated water pipe (barrel stock)

3. 4" PVC coupler

4. 4" x 2" PVC bushing (if not available combine two, like 4x3 and 3x2)

5. 4" PVC FPT adapter (clean-out adapter)

6. 4" PVC MPT threaded plug

7. PVC primer, one with dye in it if possible (purple, blue)

8. PVC pipe cement, medium body is best

The rest is provided with our SIK-201 kit.


Suggested tools for building the potato launcher:

1. Hand wood saw (or hacksaw, for cutting pipe, maybe you already got it cut at the store)

2. Wire stripper

3. Terminal ring crimper (pliers can work)

4. 3/16” Allen wrench

5. 7/16 wrench

6. Drill and ½” drill bit

7. Medium half round file for shaping pipe (or a lathe if you got one)

8. Rag for PVC cement clean up (disposable)

Step 2: Preparing the materials for assembly

To make sure everything goes together properly and smoothly, proper conditioning and sizing of the materials is necessary. Pay particular attention to the shaping of the pipe ends, as this is a major factor in proper solvent welding with the fittings.


Cut the two pipes to size, 4” dia cut 12 “length and 2” dia. Cut 48” length with the saw unless you already did so in the store. Using the file, take off the sharp corners on the inside AND outside of the pipe. Radiusing the inside helps reduce the amount of potato scud that can build up in the launcher, and breaking the outside corner ensures proper solvent welding, if this is not done leak paths may result. Cut ends should be as square as possible. To one end of the 1 1/2" pipe it is suggested that the inside be chamfered about 0.020" and the outside filed or turned down to almost meet the inner chamfer, creating a blunt knife to help size the potato.


Inspect the fitting for really bad weld lines or possible large dislocations that may result in premature failure. Remove all paper tags or labels by peeling, scraping, even using a bit of primer to clean off the last adhesive. File off any sharp spurs that may hamper your ability to grip the fittings firmly when assembling.

Step 3: Assembling the Launcher

I Chamber Assembly:

Prime both ends of the 4" pipe, also priming the 4" bushing, both 4" coupler sockets, and 4" slip fit female adapter. DO NOT get any primer on the adapter threads! Immediately apply pipe cement to the three primed 4" fittings, then LIBERALLY to both ends of the 4" pipe. Start both the coupler and adapter fittings on the pipe, start the bushing in the coupler, then right the assembly with the threads up, pressing it together with body weight while twisting about 1/2 turn. Hold this position for at least 30 seconds. The pipe ends should bottom each about 1 1/2" inside the fitting socket. If they both do not bottom, either apply more force IMMEDIATELY somehow to get it to, or you are screwed and have to throw it out--start over with that. If the fittings and pipe are properly conditioned this should not be a problem. Wipe up any spilled glue with the rag, but leave a good bead at the external pipe/fittings line. If any glue got on the threads get it out of there as fast as possible! Any glue on your hands should just be left to dry and then peel it off. Using solvent to remove it will just increase your exposure to it.

II Barrel Assembly:

Prime one end of the barrel and the 2" socket on the bushing. If one end of the barrel was chamfered to a knife, prime the square 'regular' end of the pipe. Apply glue, liberally to the pipe, and press together, again using a 1/4 turn motion to bottom. Hold for 30+ seconds. After releasing place the unit upright for several minutes, to let the glue set a little more. Solvent welding is more of a curing than a drying process. Solvent is lost, hence the term drying, but the action of the solvent effectively cures all those individual plastic parts into one continuous physically joined piece of plastic. Properly done, solvent welds are always stronger than bulk pipe.


If you are planning to paint your cannon, now is a good time

III installing the electrodes

The SIK-20 kit includes 2 electrode assemblies sized to be used where the coupling fits over the pipe. The over lap of pipe and coupling is 2” and we recommend centering the electrodes within the overlap area, 180 degrees opposing. Once you have the electrode centers marked you will need to drill ½” holes centered on the marks and exactly opposing each other. At this point the tips should be touching. (Once the terminals are attached and jam nuts tightened the well nuts will expand and electrode gap will increase… See section V)

IV Handle Assembly

Push the handle ends on the aluminum tube until its seats to the bottom. Connect the modular interface from the MRS-201 ring set and the handle assembly using the 4 ¼-20 x 5/8” socket cap bolts. Check the alignment on a flat surface. Place the ring arches on the barrel near where the barrel and chamber meet. Attach with smooth top rings and (4) ¼-20 x 7/8” Socket cap screws and square nuts


V Igniter / lead / electrode connection

Insert the electrode assembly through previously drilled ½” holes. Insert red button igniter through handle hole guiding the wires through and out the side facing the chamber. Size wires, remove insulation, slide on heat shrink, crimp on terminals slide heat shrink to insulate terminal and wire connection. Heat shrink tubing using a lighter or hair dryer. Connect igniter terminals to threaded electrode assembly in this order: washer – terminal – nut and tighten. The electrode assembly well nuts will expand in the hole and provide an airtight seal, tighten until ¼” threads are above the nut.


With chamber open and from a distance, look to check for spark jumping electrode gap. Your gap should be around 1/8” to 3/16” and produce a bright spark. If the electrodes are too close pull them out and file/grind of tips slightly to widen the gap. Once you have consistent spark its time to add the electrode covers (plastic cover with metal insert). Align over the threaded electrode end and gently tap on.

Step 4: Using the launcher

1. Now that you spark is verified, test fit the threaded plug into the adapter. It should engage the threads at LEAST TWO TURNS. If not, check for crud in the threads, and if clear, obtain a 60deg triangle diamond file, and size down the plug threads a little. The threads are at a 60deg angle, so careful filing. Usually filing the first few threads is ok.

2. With the cap off, load a potato! With the chamber on the ground, place a potato over the muzzle of the launcher, and press it down with your palm, shaving off the excess, creating a cylindrical potato plug. Make sure the potato contacts the wall firmly all around, or it will not fire or not that well. Loading the potato sideways is acceptable, as it creates a more stable projectile anyway. Ram the potato down to within 2" of the breech of the barrel, using a smaller diameter PVC pipe or broomstick. Don't push it too far or it will fall out into the chamber.

3. With the spud firmly seated in the breech, pick up the launcher and holding with one hand, dispense 1-2 seconds of Static Guard™ (hairspray works too) directly into the chamber. Don't use too much; it will just make a mess. Quickly close by screwing on the end cap hand tight, do not use a tool to tighten to two turns or you will likely never get it off again.

4. Point the launcher in a safe direction, and depress the igniter button. That potato you rammed down there should exit at a quite rapid rate with a sizable report, and depending on where you aimed and at what angle you pointed, it went anywhere from 6 inches to ~200 yards from the muzzle. If you clicked the igniter a few times and it didn't work, you are not alone, check out the next section.

5. If it worked, great! Remove the end cap (this may require a tool), vent the spent gasses getting a fresh load of air, and repeat as necessary!

Trouble shooting your cannon

There are a lot of reasons why your launcher may not be working. First and foremost NEVER take off the cap and start clicking away at the igniter.

Hairspray in cold weather just does not go well. Too much of the burnable stuff in the spray condenses on the chamber walls, making it very difficult to burn. You might consider Propane or Static Guard™

To 'defuse' a misfire you need to take off the cap, while pointing it in a safe direction. Allow the chamber to air out for several minutes, perhaps longer, to get the fuel load out. After you are certain the fuel has been vented, again verify the spark, just by turning the chamber enough so you can see where the spark should be. Never point the chamber bore directly at your face, or body, or anybody else. If it sparks then it is a fuel mixture problem.

One of the most common fuel problems leading to misfire is too much fuel! Not usually a problem with hairspray, other richer fuels can be overloaded above their UEL value, and they won’t work. Always try less fuel rather than more fuel.

If you still can't get it to work I invite you to peruse the many other web sites that talk about how to troubleshoot your combustion launcher.
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Tue Aug 18, 2009 10:50 pm

Stickied. :)
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Wed Aug 19, 2009 6:56 am

Nice how-to, but more pictures could do it some justice.
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Wed Aug 19, 2009 12:37 pm

jagerbond wrote: Trouble shooting your cannon


One of the most common fuel problems leading to misfire is too much fuel! Not usually a problem with hairspray, other richer fuels can be overloaded above their UEL value, and they won’t work. Always try less fuel rather than more fuel.
I would say that any spray fuel has the problem that it is very easy to overfuel. Nothing special about hairspray in terms of getting the fuel ratio within the combustion limits.
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