Baking Soda Gun Paper

Baking Soda and Vinegar Guns
P. Gordon Kennedy
Copyright 2009

I first thought of the idea of making a gun powered by baking soda and vinegar during the summer of 2004. I built a large and complex prototype, but it failed to fire a single shot. It suffered from the problem of being too complex, although the ultimate reason it failed, is it could not establish a tight seal and thus could not build pressure. I set the project aside until early 2005 when I came up with a much simpler prototype that actually worked.
I built my first working baking soda and vinegar gun in early 2005. The gun consisted of two eight-inch long sections of threaded ½ inch diameter PVC pipe joined together by a ½ inch threaded PVC ball valve and capped on one and with a ½ inch threaded PVC end cap. Plenty of Teflon thread tape was used on this and all subsequent baking soda guns to ensure the tightest possible seal on all joints.
Through experimentation, I discovered that a ratio of one part baking soda to four parts vinegar by volume worked best. For my gun, I used 2 tablespoons vinegar and ½-tablespoon baking soda per shot. For a projectile, I used a cork bottle stopper, though I later switched to shooting rubber stoppers.
To load the gun, the vinegar was measured and loaded into the bottom chamber of the gun and the valve was closed. Next, the baking soda was measured and loaded into the upper chamber of the gun. Finally, the projectile was snuggly fitted to the open end of the gun. To fire the gun, I first pointed it in the direction I wanted to shoot. Then I opened the valve and shook the gun vigorously (while still keeping it pointed in the direction I wanted to shoot). After several seconds, the projectile would fly out followed by a spray of the spent reactants.
In its first velocity test in the spring of 2005, the gun fired a cork at about 141 feet per second. In its first test with rubber stoppers about a year later, it only got about 77 feet per second, but that was due to the fact that the rubber stoppers I used did not fit tightly enough and allowed the pressure to escape before it had a chance to build up. Using an ultra-tight rubber stopper that took about 15 minutes to ram in, I achieved the fastest velocity I ever have with this style of baking soda gun, about 186 feet per second. I call my first baking soda gun and guns like it single-valve guns, because they have only one valve. The gun on its best shot produced about 0.69 foot pounds of projectile force for every teaspoon of reactants used.
The next major improvement to the design of the baking soda gun came in March of 2006 when I decided to build my first double-valve gun. The gun I built was identical to my first gun and used the same amount of reactants, the only difference was the addition of a second valve to the open end of the gun and in front of that a three-inch long section of threaded ½-inch diameter PVC pipe.
The double-valve gun had two major advantages over the single-valve gun. First, the second valve allowed the pressure to build up to its maximum before the projectile was fired, thus improving velocity. Secondly, the addition of the second valve allowed the gun to be aimed much more precisely than the single valve gun could be. In testing, the fastest velocity I was able to achieve with my first double-valve baking soda gun was about 195 feet per second, though the gun like the single-valve gun before it had large variations in velocity from shot to shot.
In April 2006, I further improved the double-valve gun by building a version that used six-inch long pipe sections instead of the eight-inch long ones used in the previous guns. I also shortened the piece of pipe in front of the forward valve from three inches long to 2 ½ inches long. This gun also used the same amount of reactants as the previous two guns, but was able to build much greater pressures, resulting in improved velocity.
By using a modified air compressor pressure gauge, I was able to determine that the pressures reached by this shortened gun were around 90 pounds per square inch. In testing, the fastest velocity I was able to achieve with this gun, which is the fastest velocity I have ever achieved with a baking soda gun of any type, was about 211 feet per second. This gun also had the best efficiency of any of the double-valve baking soda guns. On its best shot, it produced about 0.89 foot pounds of projectile force for every teaspoon of reactants used.
In August 2006, I made my third and final improvement to the double-valve baking soda gun. I shortened the forward chamber of the gun from six to four inches long and shortened the pipe in front of the forward valve from 2 ½ inches to 1 ½ inches. This gun was able to produce internal pressures of around 120 pounds per square inch, the highest pressure I ever achieved with a baking soda gun. In velocity testing, this gun achieved a maximum velocity of about 209 feet per second.
In an experiment, I aimed this particular version of the double-valve baking soda gun at an empty aluminum pop can. I fired the gun at the side of the can from a distance of approximately three inches. The impact put a huge dent in the can whose depth was slightly over half the can’s diameter. Additionally, the impact sent the can flying 15-20 feet through the air.
In another experiment, I shot this gun at point blank range into a Styrofoam block. The rubber stopper penetrated 7/8 of an inch into the Styrofoam. I also tried this experiment with my ¼-inch diameter 2 15/16 inch long brass gun and was able to get a rubber stopper to penetrate ¼ inch into the Styrofoam and when I tried the experiment with my smallest baking soda gun, the cork was able to make a 1/10 inch deep dent in the Styrofoam.
In July 2008, I built a miniaturized version of the single-valve baking soda gun. This gun consisted of a ½ inch diameter threaded PVC end cap joined to a two inch long section of threaded PVC pipe, in turn joined to a ½ inch threaded PVC ball valve and a 1 ½ inch long section of ½ inch diameter threaded PVC pipe. The gun’s overall length was only 5 3/8 inches. The gun used 2 teaspoons of vinegar and ½ teaspoon of baking soda per shot. In testing, the gun achieved a maximum velocity of about 125 feet per second using an ultra-tight fitting rubber stopper. Though this little gun was not the fastest I ever built, it was the most efficient. On its best shot, it produced about 0.94 foot pounds of projectile force for every teaspoon of reactants used.
In September 2008, I built an even smaller baking soda and vinegar gun. It was made of ¼-inch diameter threaded brass pipe and had an overall length of 2 15/16 inches. The gun was constructed by joining an end cap to a one-inch long pipe section, in turn joined to a ball valve and a ¾-inch long pipe section. The gun used ½-teaspoon vinegar and 1/8 teaspoon baking soda per shot and reached a maximum velocity of about 62 feet per second in testing. Its efficiency was about 0.51 foot pounds of projectile force for every teaspoon of reactants used.
Later in September 2008, I built my smallest ever baking soda and vinegar gun. It had no valves and consisted of a one-inch long section of 1/8 inch diameter threaded brass pipe joined to an 1/8 inch threaded brass street elbow and capped on the other end with an end cap. The gun shot 1/8 inch corks using only one milliliter of vinegar and 500 milligrams of baking soda per shot. It was able to achieve a maximum velocity of about 53 feet per second in testing. The gun had an overall length of 1 3/8 inches and a height of about 1 inch.
To load and shoot this tiny gun, a few drops of vinegar was poured down the barrel into the elbow. Next, a pinch of baking soda was loaded into the barrel and the cork stuffed in. To shoot, the gun was flipped over and shaken to mix the reactants.
The development of the baking soda gun also led to the creation of some other baking soda and vinegar powered devices. By attaching a rotating garden sprinkler to the front of one of the double-valve guns, I was able to build a baking soda and vinegar powered reaction turbine engine. The turbine was able to run for two to three seconds on a single charge of 2 tablespoons vinegar and ½-tablespoon baking soda.
Another device I built to run on baking soda and vinegar was a small water cannon. The device consisted of a six-inch long section of ½-inch diameter threaded PVC pipe capped by a ½ inch threaded PVC ball valve at one end and a 1/8 inch brass nozzle at the other. The tube was filled with water and screwed to the end of one of the double-valve guns. When the valve was opened, it sprayed out the water along with some of the spent reactants quickly.
In May 2007, I used the three inch long section of threaded ½ inch PVC pipe used on the first double valve gun to build a baking soda and vinegar powered airbag. I took a sandwich bag (the twist tie type, not the zipper type) and taped it securely to the pipe. I stuffed it into the pipe and covered the end I stuffed it into with a layer of aluminum foil also secured with tape.
To deploy this airbag, I loaded one of my double-valve baking soda guns with a standard charge of 2 tablespoons of vinegar and ½ tablespoon of baking soda. Instead of the pipe section used to hold the projectile, I screwed the pipe containing the airbag into the gun’s forward valve. After reacting the baking soda and vinegar, deploying the airbag was a simple matter of opening the forward valve. The airbag inflated in less than 1/10 second with a loud bang, shredding the aluminum foil in the process.
In the fall of 2008, I built a shot shell to use with my double-valve baking soda and vinegar guns. The shell was made from a 2 ½ inch long section of threaded ½-inch diameter PVC pipe. A rubber stopper was placed in the bottom of the pipe and approximately 25 small steel ball bearings were loaded inside. The top of the pipe was capped with aluminum foil and tape.
To shoot the shot shell, a double-valve baking soda gun was loaded with a standard charge of baking soda and vinegar. Then, the shot shell was screwed into the forward valve (aluminum foil end facing outward). After mixing the baking soda and vinegar, the forward valve was opened to shoot the shot and rubber stopper. When shot at a target six inches away, the shot had a spread of about three inches. The overall range of the shot shell is much shorter than using a cork or rubber stopper alone, but it is powerful at close range and is able to embed its shot into a Styrofoam block when shot at six inches.