How To: Smash the Summer Heat with These High-Powered DIY Water Weapons

Smash the Summer Heat with These High-Powered DIY Water Weapons

This summer's going to be a hot one, so skip the water pistol this year and break out the big guns! In this project, I'll be showing you how to build a water balloon shotgun—a high-powered water balloon launcher that's capable of firing 17 water balloons at the same time!


Adult supervision and adequate training is recommended. Misuse, or careless use, of equipment or projects may result in serious injury, property damage, and/or death. Use of content is at your own risk.


This water balloon launcher is done with either a simple modification to my previous Rocket Rifle project, or as is with my other high-powered project, the Candy Cannon. Click on the links for written step-by-step instructions, or just watch the videos below.

Modifying the Rocket Rifle

To modify the Rocket Rifle into a Water Balloon Shotgun, all you'll need to do is unscrew the barrel and replace it with the cannon adapter.

The cannon adapter is simply a 2 foot length of 2 inch PVC pipe, a 2 inch coupling, and some reducer bushings to bring the threads down to 1 inch. Lastly, a 1 inch close (short) PVC riser, so that it will screw into the sprinkler valve on the rifle.

I added some camouflage paint to match the gun.

Image via

Firing Water Balloons from the Modified Rocket Rifle

When shooting water balloons, one challenge you need to be aware of, is how the pressure from the gun bursts the ballon before it even gets out of the barrel. There are four steps you can take to get a successful launch.

Step 1: Wadding

You need something that will cushion the pressure on the the balloon as it's launched. I made some wads with plastic cups. They are firm, but cushion the balloon enough during the acceleration to keep it intact. You could also use cloth, or even as something as simple as a moistened rolled up sock.

You can use the barrel from your rocket rifle as a ram-rod to push the wad to the bottom of the barrel. It should be as close to an air-tight fit as you can get.

Step 2: Lubrication

If the barrel is dry, the balloon will pop when it's fired. This is because of the friction during payload acceleration.

I found that using a bit of vegetable oil to coat the sides of the barrel eliminated this problem. It also helps lubricate the diaphragm in the sprinkler valve to prevent it from locking up.

Water works as lubrication as well, but over time, the minerals from the water will dry inside the valve and may make it lock up at higher pressures, to the point where the 9 volt battery isn't strong enough to open it.

Step 3: Balloon Size

The smaller the balloon, the stronger it will be. I had great results with balloons that had a slightly smaller diameter than the barrel. If they are wider than the barrel, you can still make them fit, but there will be more friction as they exit, and a greater chance of failure.

Step 4: Using the Right Pressure

I found that 65-70 PSI works great for a single water balloon. At this pressure, you can expect a balloon to fly around 300 feet!

You can fit multiple balloons in the barrel, and will need to adjust the pressure up slightly with each one you add.

I tested all the way up to 17 balloons at 90 PSI with great results!

The 2 foot barrel will hold around 17 water balloons. This increases the weight of the payload significantly, so a pressure of around 90+ PSI is recommended for longer distance shots. Otherwise, they will just plop out of the end. Funny, but not very effective.

Other Thoughts

There is quite a bit of kick as the balloons are fired out, so using the Candy Cannon as a Water Balloon Mortar is the easiest option, and the barrel can be tilted for trajectory.

However, using the Rocket Rifle to shoot multiple balloons, has a great and powerful feeling to it that you can't get with the Candy Cannon.

For portability, the manual ball valve near the fill port can be closed, maintaining the pressure charge in your water weapon. It will probably only be good for 1 shot, but will give you the option to disconnect from the air hose and go anywhere. The pressure charge should hold indefinitely.

That's It!

Well, there's one way to get out and take advantage of the good weather this summer—and be cool at the same time. If you haven't seen the video yet, you can still see it here. And if you missed seeing how to build the Rocket Rifle and Candy Cannon, be sure to check them out as well.

If you like this project, perhaps you'll like some of my others. Check them out here on WonderHowTo or at

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