Weak Sparks Need Not Apply
Experiments performed a few years ago and shown on the web page here found that weak sparks, such as from static electricity, are incapable of igniting black powder. Since I wanted to use smokeless powder in the rifle, and since it has a much higher ignition point than the black powder shown here, my first attempts used sparks from a stun-gun to see if they could ignite the powder.
Even Strong Sparks Are Wimpy
The stun gun shown here is advertised as producing a 100,000 volt spark. The sparks
were certainly loud and impressive, and they easily burned tiny holes through a piece of paper placed between
the electrodes, but would they ignite powder?
Hundreds of sparks were struck into a pile of Hodgdon's Tite-Group smokeless powder (left) and Swiss black powder (right) with absolutely no effect except for bouncing the grains around. The sparks were striking the grains, and you can see flashes when the spark hits the surface of the granules, but never once would the powder ignite!
The photo below shows a spark from the stun gun going completely through a line of black powder stuck to a piece of masking tape, and although hundreds of grains were simultaneously hit, nothing happened.
Corraling The Granules
My first thought was that the granules were simply being blown out of the way, and if the powder was confined (loosely packed) in a breech, they would be held in place and therefore ignite. To accomplish this, a breechplug was made with a spark-plug like tip. An insulator was cut from ZTA ceramic ("ceramic steel"), and contained a central electrode connecting to the spark source - in this case, the stun gun. As you can see here on the right, there are nice, hot sparks inside the collar, which is used here as a substitute for a barrel.
However, when the smokeless powder was packed into the space around the electrode, passing sparks through it as seen here had no effect. Some granules were 'popped' up into the air, and a faint spark can be seen under the powder, but nothing else happened. The same thing was tried with black powder, but still no ignition. My conclusion was that it is virtually impossible to set off gunpowder - either smokeless or black powder - with any type of spark source. However, there is an electrically fired muzzle loader, the CVA® Electra TM, so there must be a way of doing it.
My first venture into electrically fired rifles was this black powder breechloader with electric ignition. It uses the conductive properties of graphited black powder to heat the granules to ignition with a 300 volts from a photo flash capacitor.
As voltage is applied to the black powder packed in the chamber around the electrode, the current flows through the graphite coating of the granules and heats them to their ignition point. The current source used in that rifle is a 330volt 120 μfd photo flash capacitor, which can hold about five watt-seconds of energy - plenty of power to heat up that small amount of powder. Because the current is dumped so quickly, the ignition is instantaneous. The photo to the left is of about one grain of Swiss BP being fired using this principle. However, this will not work with smokeless powder since it is practically non-conductive.
The image to the left shows a high voltage power supply which can run off a 12 volt battery and puts out 7,000 volts of high frequency alternating current. It can deliver about seven watts, and the arc it produces is very 'smooth' and does not displace the powder granules. The photo to the right shows an arc that can be struck from its 'hot' wire.
Here is a test of the HVAC system setting off smokeless powder in the test fixture. On the upper right side of the image you can see the spark jump to the clip, where it then travels to the igniter and sets off the powder. This is the system I used in the fourth version of my rifle, and it very effectively sets off the smokeless powder charge - but with one 'small' hitch... Because the power from the supply can't be delivered in one quick burst, it takes a perceptible delay between the trigger contact and firing - more like a slow flintlock than the instantaneous firing that I wanted, so I continued to experiment to find a solution to that problem.
Wimpy Sparks on Steroids
Although the resistance heating provides instant ignition, since smokeless powder (and most BP substitutes) don't conduct electricity, they won't work in this scenario. However, if we can 'coax' the charge from the photo flash capacitor through a non-conductive powder in the igniter, this might be enough to set it off, and there is a neat trick to do this. Once an electric spark is started in air, the ionization created greatly lowers its electrical resistance, and in theory, it should allow the energy from the capacitor to follow along, converting a weak spark into a real powerhouse.
Here is a small spark coil I wound (directions below) which, when powered by discharging a small capacitor through the outer primary windings, produces enough voltage in the inner secondary windings to jump the gap in the igniter. The spark shown here, although it looks bright, is not very powerful and can't set off any powder by itself. However, if we hook this coil in series with the photo flash capacitor, the current from the capacitor will flow through the coil and across the gap bridged by the spark, hopefully turning a 'wimpy' spark into a real banger which will set off the powder.
Just one little problem with the augmented spark configuration was that the voltage from the capacitor (now 550 volts) was always present on the igniter and thus could have been a severe safety problem. Also, it meant that any conductive powder might be instantly fired as soon as it was added, so I had to include one more component, a spark-gap switch in series with the igniter.
The switch is nothing more than a pair of 1/8 inch stainless steel electrodes held just far enough apart so the capacitor voltage can't jump the gap all by itself, in this case, about 0.020". When the trigger spark is set off, it jumps the switch gap as well as the igniter, and the current flows through everything, but until the trigger spark goes off, the igniter is 'disconnected' from the voltage source, keeping everything safe.
The results are seen to the left, with a spark in air - just like the unaugmented spark above. To the right is a photo of an augmented spark in the igniter. The spark is hot enough to blow off pieces of the electrode! Now, if we add a little smokeless powder, it should finally ignite - shouldn't it?
Here, a small smokeless powder charge was placed into the collar and held down with a light plastic 'tamper' so the granules would stay in place when the spark hit. The right-hand side of the image shows what happened when the spark was fired - the concussion from the spark blew the tamper out and scattered powder granules all over, but the powder still didn't light!
About this time I was ready to give up, but after a few days of reflection, I thought I knew what was happening. The spark in the chamber was clearly extraordinarily hot and was vigorous enough to blow the tamper out of the chamber, which meant that the air in the chamber had to be heated to a high temperature. But why didn't the powder ignite? I believed the reason was the extremely brief duration of the spark; in trying to capture it on a video, it was so brief that it took many tries to accidentally capture a video frame on a camera running 30 frames/second. My guess is that it lasted only a few micro seconds, and thus, no matter how hot it was, it couldn't transfer enough heat into the powder granules during this brief time period for them to ignite. Therefore, slowing down the spark, even if it meant reducing its intensity, might be enough to do the job.
To slow down the spark, I simply added a resistor in series with the capacitor so the current was limited to about two amperes - which is still a lot of current going through a spark. As you can see from the image,the spark was much brighter than from the spark coil alone, but was very much less intense than without the resistor. However, it seemed to last a bit longer - about 2000 micro seconds, so that elongation might do the trick.
I added some smokeless powder (this time without a tamper) and sparked it. It worked! Not only did it work for the Tite Group smokeless powder, but for all others I tried, and all ignitions were instantaneous.
Hodgdon 'TiteGroup' Smokeless
777 Black Powder Substitute
Goex Black Powder
After I clean up my mechanical drawings and publish this material, I plan to incorporate this new ignition system into my caseless ammunition .22 rifle - which will also be published with a video when it is finished.
For those readers who insist on risking life and limb duplicating these results, a document containing the schematic and other construction details can be had by right-clicking on the schematic. The bobbin used to wind the trigger transformer can be 3-D printed by downloading this file and sending it to ShapeWays, who will print it for a modest amount. If you want to machine one, see the drawing here.
|Click on the image to see a video about these experiments.|