Firecracker Guns - a Lesson in Gun Development

This is my latest development of something I've been working on for several years. It's a firecracker-powered airsoft gun. The story about what it took to get to this point is a little interesting.

It all started back when I was 14, during the summer between junior high and high school. I had been into airsoft for several years by then but I was never satisfied with the guns I could afford. They were mostly plastic and wore out fairly quickly. The spring guns were all "sniper rifles" (or they were cheap copies of assault rifles that were spring powered), the electric guns used batteries and had complex motors, and the gas-powered guns were too expensive. I had an old sniper rifle barrel that I had gotten out of a friend's broken gun, so I stuck a firecracker and a BB into the barrel and lit it. I just had it set on a railing pointing at a tin can. It fired, sent the BB through both sides of the tin can, and I was hooked.

Then I decided to put a breach on it. To do that I took a piece of wood, taped the barrel to it, and slid a piece of pipe over the back. The rim of the pipe created a breach, and it would slide back and fourth to allow loading. It worked well, but I wanted a true pistol and not just a "hand-cannon" looking contraption. So I went and cut a branch and fit the barrel on it with hose clamps (keep in mind the barrel is about 16in long). I used a hinge with one end bent upward as a breach. It was totally unlocked. When the firecracker went off it would fly open (which was okay for a while). I eventually cut the barrel in two and mounted the halves side-by-side. It stayed in that configuration for the next few years. I used it in several battles. My friends were always fearful of it. Not only was it unpredictable and hard to use because of the firecrackers, but it was incredibly powerful. But throughout high school it stayed in relatively the same configuration.

It was only about a year ago that I finally got the urge to start working on it again. I had created several rifle-shaped wood pieces for rubber band guns that I had made, so I fitted a long barrel and a bent hinge breach to the rifle. This time I knew it needed to be locked, so I wrapped a piece of string around the hinge to keep it in place. It worked fairly well, but it blew hot gas and debris into my face when I fired. But fire away I did! It was powerful and more accurate than the pistol. However, senior year was heating up so I let it collect dust. Finally two weeks ago I picked it back up.

The new main problem was finding firecrackers that would fit in the barrel. I created a prototype of the rifle using the old method - the firecracker directly in the barrel - first, with rubber bands to lock it. However, I knew I was running out of the firecrackers that would fit in the barrel. I had tons of firecrackers that wouldn't though. I knew I needed to make a chamber to put them in. I had messed around with cut up rifle casings years earlier (for an under-barrel shotgun attachment for the first pistol which ultimately failed). So I took my remaining long barrel and fit a chamber made of an 8mm Mauser shell with the rear cut off. I changed around the design of the hinge breach to fit the rifle better (first prototype seen below) and then used rubber bands to lock it again. The new firecrackers were more powerful, and blew the breach wide open (I wasn't holding it. I don't test new actions by shoulder firing them). Then my mom suggested that I use a U-shaped piece that's hinged to hold the breach shut. I took an old hack saw blade and bent it to find, and it worked. To seal the breach better I wrapped the hinge in duck tape.

I shot around with that for a few days, doing all sorts of tests. I had no sights, just a barrel covered in duck tape to line up on. It wasn't at all ready for anything close to a battle. So today, I cut up another one of my old rubber band guns to create the second prototype. I wire-wrapped the barrel on (with duck tape just to be sure it stayed). Basically it's the original prototype but with simple sights and much better construction.

What happened next exceeded all of my expectations: I hit a man-sized target at 30 yards and a roughly 4x2ft target at around 50 yards. I didn't expect that kind of accuracy at all.

Now I'm going to start working on refining the breach lock and creating a better seal, as well as better sights.

My ultimate goal is to create a bunch of rifles and pistols to use with friends in battles. I'm not sure if I'll be able to find enough barrels (or tubing to make barrels) but I'm going to try. This project is nowhere near over, and is growing every day.

The #3 prototype I created a few days ago (before this was the original from a year ago, and then the new one last week with the first style of chamber - firecracker directly in the barrel). Next to it is my original pistol in its original unlocked configuration.

This is the new breach, loaded and ready to go, but unlocked.

And then locked (notice the hack saw blade)

A firecracker sitting in the #3 style prototype chamber.

A side view of the action.

The #3 prototype during early testing. The sling was made of cloths line.