How to make a safe projectile

37mm or 40mm

Written by GROG

This is going to be an instructional page on projo construction. Note that this is not the only way to make projos, just an easy, simple projo I've come up with, which will be safe under normal loading conditions. If you decide to use these projos, follow instructions carefully. Read over the safety page on this site prior to any round construction.

This projo design can be used with a number of 37mm and 40mm casings. Smokeless or black powder, or booster casings work great with these projos. There are differences in construction though. Pay close attention to the materials used in construction, and methods used.

Materials needed:

1. Good quality cardboard tubing, 1/8" thick sidewalls. (Available from Skylighter or Firefox)

2. Quality 5/8" solid plywood. (Important that there are no voids in the wood) For pusher wad.

3. Gorilla glue

4. Cannon fuse (quality 1/8" time fuse)

5. End cap (Either plastic or thin wood)

6. Cardboard wads, latex paint

Steps in construction:

  First, you will need to cut the tubing to a good length for the casings you are using. I find it's best if the projo ends 1/4" below the lip of the casing. (Take into account the length of the wads and pusher wad!) Keep in mind, that for good smoke signals, you will need a longer tube, and for flares, shorter tubes are recommended so as to avoid forest fires!

  Use a hole saw in either a drill press or hand drill, to cut pusher wads which are the same size as the OD of the tubing. You can use a gasket cutter set to cut some cardboard wads. You will need these to seal the end of the casing. I use 2 or 3 per round.

  Next, if you are using smokeless casings, I use a hot glue gun and glue a copper disc to the center of the pusher wad. (They cost .01c each...) Then, if using smokeless casings, drill your fuse hole slightly off center, and gorilla glue a 1.5" length of cannon fuse in place. Leave 1/4" of the fuse sticking out the bottom of the pusher wad. If you are using other types of casings, you can skip the copper disc and drill the fuse hole centered. Do up a batch of 10 or 20, and let them harden. (Use gorilla glue sparingly, but make sure it goes into the fuse hole to secure the fuse well.)

  Once the pusher wad is hardened, put a ring of gorilla glue around one end of the tubing, and mount the tubing on the pusher wad. Keep in mind, Gorilla glue expands a lot while drying, so cover your work area! Allow this to harden. You now have a projo that is ready to be loaded!

   These projos can be used for smoke, flare, or starburst, and gas rounds. Add your filler material, and you can use either a plastic end cap, or a thinner wooden end plug to top off the projo. If using plastic, use a good epoxy to seal it. Gorilla glue does not work well on some plastics. Here's a photo of the projo:


Notice how there is a small amount of gorilla glue coming out of the left side of the fuse hole. This is needed to make sure of a positive seal. This projo has a small payload area, and would be used for flares or a small star burst. This is a 37mm projo, but the same method is used for 40mm.


Here's an example of a 40mm projo with a different end cap. Sides of seal are wrapped with a little electrical tape to aid in sealing the sides of the projo.


With these diagrams and photos, you should be well on your way to making good, safe projos for your launcher. Make sure that when you buy your tubing and make your wads, when completed, the projo slides freely through your barrel. Many launchers have larger chambers, but smaller barrel diameters. Be aware that if the projo gets jammed in the barrel, it could rip your barrel off! 


Here's how you want you're projo to fit in your smokeless casings. You want to try to get the fuse to go right into the vent hole. This will keep your powder in, and aid in lighting the fuse. (This casing is sawed off. When loaded in a real casing, the projo would be below the end lip of the casing, and sealed in with two cardboard wads, and latex paint.)

For black powder casings, they can be loaded the same way, except cut your fuse on a 45 degree angle and split the end to aid ignition.


Never use explosives in ANY 37mm or 40mm reloaded projectile! Read the safety page!



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Copyright 2002-2004 Grog's 37mm and40mm Information
Last modified: 10 MAR 08