This is a real easy thing to make, and also so cool, my friends and I made this as a school project taking about 1 week.
Step 1: What You Need
This is a bout a $40 Project easy to make
You will need:
-1 1/2' long 3" diameter abs pipe
-3' long 2" diameter abs pipe
-3" to 2" diameter reducer abs pipe
-3" diameter abs cap
-3" diameter abs cap screw
-a gas grill igniter from Home Depot
-a nail or 3" diameter drain with large holes
-abs glue ONLY ABS NOT PVC(it is called black abs)
-3' wooden dowel (used to push potato down)
Step 2: Let's Start
First lets take the 3" diameter drain, and the abs glue and put it in the 3" diameter side of the reducer and stick the drain in and put more glue around it.
Now put glue on the rest of the 3" diameter side of the reducer and we can take your 1 1/2' long 3" diameter abs pipe and stick it in the 3" diameter side of the reducer with the glue until it doesn't go anymore in.
Now put glue on 2" diameter side of the reducer, and stick your 3' long 2" diameter abs pipe and stick it in that until it doesn't go in anymore.
Now finally take the 3" diameter abs cap and put the glue in on the inside of the cap until the part you screw in the cap screw in, and put this around the end of the 3" diameter abs pipe.
LET THIS ALL DRY AND SET (3-6 Hours)
Step 3: Finalization
Now with your grill igniter, or the "sparker", and there should be two long wires that have metal pieces on the end that create a spark when you hook them up to the spark button. When this sparks consistently. You will drill two holes as big as you need to get the two metal pieces in, and get them in and try sparking (you may have to bend the larger piece of metal up). When you see them spark, you are good and just tape them down or use the abs glue to make them stay.
This is what will create the EXPLOSION!
Also you may want to grind down the end of the 3' 2" diameter abs pipe, until sharp, just to cut down potato.
Step 4: Shooting
Alright, now that everything is set and ready, you get to do the fun stuff... SHOOTING
But first, let's make sure every thing is good, as I was told, "You can never be too safe!" And I learned this the hard way when my friends screw cap came off and just missed me hitting my shirt ripping through it, and burning me, so you should shoot this from the ground like a mortar, or from the hip where nothing can hurt you. Alright, now let's go!
Now we put the potato in the 3' 2" diameter abs pipe, and smash against ground to cut potato until inside, and get down in pipe until it goes down all the way. It should be real tight.
Now let's unscrew the the cap screw, and spray about three shortish bursts in, and screw it back on.
Now hold... Prepare... ANd... Click the igniter button.... BOOM!!!
If it shoots, congrats, if not just keep pressing igniter button about 4-5 times, and regroup and spray some hairspray in and try again.
Congrats, you just made a potato gun :)
Step 5: Q's
If you have any questions, I will be happy to answer them. :D