Introduction: Pneumatic Snowball Cannon

New England just got it's first snow, now to make use of it. I know a lot of people make Potato guns, which are pretty much the same, but I find shooting food pretty pointless. Snowballs are funner, and less destructive. Your total cost for this will be about $45, if you already have an air compressor. If you don't, you'll have to buy one, which can be costly. I had a compressor, but I just wanted to get a new one.
All the parts used in this instructable came from Lowes, except the compressor. The photos are tagged with the part number and price from lowes.

Gun in action:

Second version gun in action:

IMPORTANT: Skip to last step for a slightly more expensive, but better version.

Step 1: Get the Parts

Most of the parts are made by Kobalt, which is the Lowes version of Craftsman from Sears. They're pretty good quality by my standards.
The air compressor was from Sears, it's the Craftsman 1hp 3 gal. Air Compressor.
You can choose to build a 2 inch pipe model, or a larger one, either 3 or 4 inches. You'll only have to get a different size cap and pipe size.

Here's the list from Lowes:
- (Two of these) 1/4 to 1/4 Male coupler - $2.19 - #2270 (Their image is incorrect)
- 1/4 to 1/4 Female coupler - (Not sure of the price or where go get one, it came with my compressor)
- 2" PVC cap - $0.52 - #23406 (Not available online, easy to find elsewhere)
- 1/4 mini ball valve - $7.96 - #221029
- Pressure Gauge - $7.94 - #221022
- 7/16th drill bit - $7.58 - #219842 (Not available online, and you can find them anywhere, probably cheaper too)
- 1/4 NPT Tap - $9.97 - #232530
- 2"x5' PVC Pipe - $3.97 - #23833 (Not online, but easy to find)
- Compressor air adapter - Depends on what kind of compressor you have. (It'll most likely be a 1/4th NPT thread)
You'll also need an old, empty propane tank. If you don't have one, you can get an oxygen tank from Lowes for about $5. Thats the cheapest kind of tank you'll find.

For tools, you'll need a grinder (Or a hack saw), some vice grips (Or a tap wrench), a cordless drill with a clutch, a 5/16th ratchet socket thing, and some misc Allen wrenches.

Step 2: Burn Off the Propane

You will need a 100% empty propane tank to do this, otherwise, you'll have some interesting results when you start drilling.
I just lit my torch, and left it underneath my porch, where we store fire wood. It's the only place that's outside, not covered in a foot of snow. Thank god nothing caught fire.
Do NOT do it inside, burning Propane lets off Carbon Monoxide, and burning out an entire tank, or even half a tank, could let off enough to kill.

If you use oxygen, I guess you can just let it out.

Step 3: Drill Your Hole

This first hole is going to be for the pressure gauge. I didn't have a center punch, so I used a Phillips screwdriver and a ratchet. You want to make 2 holes, one for the gauge and one for the air inlet. I put them opposite of each other on the bottom of the tank.

When you drill, I suggest first making a smaller hole, followed by the big 7/16th one.

Step 4: Tap Those Holes!

Time to tap the holes. I like to fasten my taps in a vice grip as illustrated in the second picture. It holds it way tighter than the other way, surprisingly. And a side note, do NOT loose your tap inside the cylinder. It is no fun at all to fish it out. I accidentally lost mine, and I had to fish it out with a magnet and some needle nose pliers.

Step 5: Put in the Gauge and Inlet

First wrap the threads in Teflon tape, just for good measure. Don't use too much tape, just wrap it around the threads twice. Too much will rip off when you screw it in. And also beware, if you over tighten it, it will mess up your threads, because the metal isn't that thick.

Step 6: Modify the Ball Valve

The ball valve is designed to stop after turning 180 degrees, which isn't what we want. This, like a normal ball valve, is open with a quarter of a turn. 180 degrees is 2 quarter turns, so it starts on off, and stops on off. You need to take out the hack saw or grinder for this step. First, you have to take off the bolt that holds on the lever. Then chop off the section shown in the first picture.

Step 7: Create the Automatic Firing Mechanism

You obviously can't open the valve fast enough, being a human and all, but don't worry, I have a solution for that. First, you will need a 5/16th socket, from a ratchet. This should fit perfectly over the bolt for the lever on the ball valve. If you're using another ball valve, just find one that fits.
Now, check if that socket fits in your drill. If it does, you're all good. If not, you'll have to do what I did. Find an Allen wrench that fits into the opposite side of the socket, and make sure it doesn't spin when you put pressure on it. Do not try to over turn it, you'll strip the threads. I stripped mine, but all I had to do is take off the washer and use the threads there. Anyways, once you make sure it fits, you'll have to cut off the shorter half of the Allen wrench, so that it spins right. The first picture is the valve with the socket and wrench all set up. You can use a hack saw or a grinder, I choose grinder for this one, because it's less delicate. The long side of the allen wrench will go into your cordless drill, to fire. This is why you need a clutch drill, you have to put it all the way on 1, so it'll open the valve and start slipping when it hits the stop.

Step 8: Drill and Tap the Valve's Hole

I decided to drill a hole in the top of the propane tank, so the entire thing looks streamlined. It took a while to drill through the top, and its harder to tap, but it's worth the better look. For this one, I just went straight in with the big drill.
When you're done, this hole will be hard as hell to tap. You'll need LOTS of wd40, i used half a can, and you'll need to do a reverse turn every 3 turns. I even managed to dull my tap on it. Oh well, gives me a good reason to return it, I guess.

Anyways, once you're done tapping, you should put some Teflon tape on, and screw in the valve. I had to grind the handle down a little, so it doesn't hit the tank on the way down.

Step 9: Pressure Test

Just to make sure it can hold pressure, I'm trying it on 40 PSI. Check out the video.

Step 10: Modify the PVC Cap

Drill a hole in the cap with the 7/16th drill bit, make sure its in the center, otherwise your snow ball will spin. After that, tap it, and thread your second 1/4 to 1/4 male coupler through it, making sure that you're threading from the side that will end up on the inside. Once all the way through, attach the female to female connector to the male to male one. This will connect the PVC pipe to the air tank. The picture is of the finished connector, I forgot to take pictures of the process.

Step 11: Glue the Cap Onto the Pipe

Clean the pipe with the pipe cleaner, then clean the cap. Then apply glue to the cap, and put it in. Don't get glue on your fingers. It sucks to get off.

Step 12: Assemble Parts

Screw the cylinder into the PVC pipe. You should be done.
I choose to duct tape a piece of wood to both the tank and the PVC for support, since that cap can't hold a lot.
I later found out that that cap, was a piece of crap. It broke on me.

This is what version 1.0 looked like, 2.0 is on the way.... with improved PVC pipe, and using only one drilled hole at the top of the cylinder.

Step 13: Version 2.0

I didn't want to write a whole new instructable, but with some extra hardware, you can make a much better version.
One of my friends leaned against the air inlet, and caused it to break out of the threads. So that inspired me. This only has one hole drilled, in the top. It's way more reliable. There's about an inch of metal to tap, compared to a millimeter. The improved version is also portable too.

You'll need these additional parts:
- 1/4 npt female to female coupler
- 1/4 npt 3 way adapter (2 of them)
- Second ball valve
- And possibly a new tank.