If you're looking to own a rocket launcher, either for use in a game or for bragging rights, it's simple on how to make your own safely and cheaply.
Here are the things you will need for the launcher
5 feet of pressure rated 2 inch PVC pipe [$4]
2 - 2 inch couplings [$1 each]
2 - 2 inch bushings that reduce down to 1 inch [$1 each]
6 inches of 1 inch PVC [$2]
1 - 2 inch end cap [$1]
1 - 1 inch sprinkler valve (with solenoid) [$15]
2 - 1 inch threaded adaptors (should be included with the sprinkler valve) [$1 of not included]
1 - tire fill valve (for car tires or bike tires depending if you have an air compressor or a bike pump) [$2.50 for 2]
1 - large project box [$3]
3 - 9v batteries [$10 for 4]
1 - bag of wiring for 9v batteries (to make a relay) [$5]
1 - momentary switch [$3]
TOTAL COST OF MATERIALS: About $50
Table saw/ hand saw
PVC cement AND primer [$5 each]
To make the launcher, you need to make two components. The barrel and the pressurized valve assembly.
To make the barrel, cut the 5 feet of 2 inch PVC pipe in half (2.5 feet) with the table saw. Prime and cement the 2.5 feet of tubing to a coupling and a bushing. Cut 1 inch of 1 inch PVC pipe. prime and glue this into the end of the bushing. On the other end of the one inch segment, you will prime and glue the adaptor for the sprinkler valve. Add some teflon tape to the threads and screw it on to the valve. Make sure that the flow direction is in the proper direction, or the valve will not work. Then screw the barrel into the Sprinkler valve.
For the pressurized section, you will need the remainder of the piping. This will be your air reservoir. I used tire fill valves on my launcher. Drill a hole in the center of the dome on the end cap that is just smaller than the tire valve. Push the valve into the hole an make sure that it is snug. Apply some epoxy around the edges of the seals. apply the primer and glue to the end cap and push it onto the remaining 2.5 feet of 2 inch pipe. On the other end, glue on the coupling and the bushing and another 1 inch segment of 1 inch PVC pipe with a threaded adaptor. (same way the barrel was set up). Add teflon tape to the threads and screw it into the sprinkler valve.
Your launcher is almost done. Please allow at least 2 hours of dry time before pressure is applied.
so that you can release the pressurized air and launch your projectile, you will need a way to activate the solenoid. I did this with 3 - 9 volt batteries, the wiring, and the momentary switch. The solenoid will have two wires coming from it and the momentary switch will have two contacts. The direction of flow does not matter, the solenoid will activate the moment it has a current of 24 volts. Your wiring assembly should like like this: wire from solenoid connected to one of the terminals for the 9v battery, that will be connected to the next terminal, and that will be connected to the last terminal. You should have one long wire with three batteries connected at this point. the end of the long wire is then connected to one of the terminals on the the momentary switch and the other wire from the solenoid will be connected at the last terminal on the momentary switch. you will need to drill 3 holes into your large project box, two for the ingoing wired from the solenoid and one for the switch. Your wiring is complete!
Attach the project box to the launcher some way, i used two large zip ties.
The projectile. This launcher can shoot many things; water balloons, nerf pocket vortex footballs, airsoft bbs, etc. I used nerf footballs because of the fins. I added weight to the nerf football by mixing hotglue and bbs by cutting the football open and gluing it back together with hot glue. I tested the rockets at various pressures, and I found that 80-85 works best for my projectiles. At 85 psi, I was able to launch an altered football about 150 yards.
for about $60 (with two rockets and other misc. supplies) you can have a very effective and accurate single shot rocket launcher (maybe a mortar too) for a low cost.