An Electrically-fired Black Powder Rifle

Disclaimer:

The material presented here describes the construction of a device which has the potential to cause harm through its improper construction, maintenance or use. The author presents this material solely as a record of his personal experiments and neither encourages nor discourages like experiments by the public. The information presented here is believed to correct, but the author makes no representation whether an identical or similar construct would or would not cause harm to the user. Duplicating this or similar constructs should be only done in accordance to national, state and local laws and further should not be undertaken by persons inexperienced in such work.

Purpose:

Well, the main purpose was to see if it could be done. It started out when I wanted a squirrel-caliber rifle that was really cheap to shoot and could be used off my porch without disturbing (or endangering) the neighbors. Outside of an air rifle (of which I have a few), that pretty well describes a .22 caliber rifle with a Flobert cartridge (BB-Cap or CB-Cap). However, I also didn't want to litter the porch with spent brass, so I began thinking of the feasibility of a .22 caliber muzzle loader.

Evolution of the Design:

I shoot (almost) only flint, but that didn't seem practical in this caliber, nor did percussion, because the tiny powder charge wouldn't even fill the drum on a regular percussion barrel. In thinking about it some more, it didn't seem reasonable to have a muzzle loader either, because putting down a patched ball (or even unpatched) would be almost impossible unless I cleaned it after each shot, and this would defeat the purpose of a simple, fun 'plinker'. I then began considering a variation on a Queen Anne screwbarrel pistol design, where an oversize ball is loaded in the breech on top of a powder charge, and the ball is 'swaged' into the barrel when the pistol is fired. This produces a lot of power because the pressure builds up quite a lot before the ball begins to move. I decided to use #4 buckshot, which is .240” in diameter (20.7 grains), in a 0.250” diameter chamber holding about two to four grains of 4F powder. The transition from the chamber to the barrel was coned to allow smooth swaging of the round shot. This seemed to be a good approach, but I still needed a way to light off the powder charge. I decided to see if it could be done electrically.

We have all heard stories about “how sensitive black powder is to a static spark”, so setting it off with a spark from a ceramic igniter seemed a great way to go. However, it didn't work at all – the results of these earily experiments are shown here, and are interesting reading in themselves: http://www.ctmuzzleloaders.com/mlexperiments/sparks/sparks.html.

These tests did point to another method; in performing the experiments, I had measured the resistance of a lightly packed pile pf black powder and found it to be about 1000 Ohms. When you apply a voltage to something that conducts, current passes through it and some of it is dissipated as heat. The formula for this is Power (watts) = Voltage*Voltage/Resistance. If I put 100 volts through that pile of powder, I get a power dissipation of 100*100/1000, or 10 watts. It's not much, but in a tiny pile of powder, the heat builds up and will ignite it almost instantly. After playing around with it a bit, I decided to use about 200-300 volts to ensure almost instant ignition.

The only design questions remaining were “details”, like how to actually build it. I ultimately decided to use a bolt-action design utilizing a Ruger 10-22 barrel and stock, with a custom-machined receiver and “bolt”. The power supply was scavenged from a disposable camera flash system, which provided the 200-300 volts required and could be operated from a single battery. The next critical design considerations involved safety issues and the need for a gas-check mechanism.

Keeping it Safe:

Using only four grains of black powder in a modern stainles steel barrel, I had no concerns about blowing the barrel no matter what the circumstances, but there were safety issues concerning blow-back from the gas check, integrity of the bolt itself and of course, user safety issues, such as making it impossible to shoot unless the bolt were fully closed. The blow-back problem was taken care of by providing a semi-sealed expansion space between the breech and the bolt, so even a full blow-back of the powder gasses would be given some room to expand before being safely released at a right angle to the barrel and away from the shooter. Although it is highly unlikely that the 3/8” stainless steel bolt arm could be severed, or that the chamber plug could be pushed backwards through the bolt, if they did, they would be aimed right at the shooter's face. To solve that problem, I added a thick stainless steel plug at the back of the receiver to catch anything coming that way. These can be seen in the schematic drawings of the action (Figure 1). A conductive stud was placed in a plastic insulating ring at the back of the bolt to provide the electrical connection between the firing plug and the power supply. Since the connection is made only when the bolt is fully forward and closed, that arrangement also prevented firing unless the bolt was fully locked.

Hot Powder Gasses – Check Yours Here!

Keeping the hot powder gasses in the barrel where they belong is not a problem with a muzzle loader (unless you count some loss through the vent), but a cartridgeless breech loader is a different matter. Not only do you not want gasses blowing back at you, but they also carry debris which can foul the works. My first attempt used a plastic sleeve at the end of the firing stud, with the conductor going through its center. That's not quite as stupid as it sounds; remember that shotgun shells are made from plastic, and rather cheap plastic at that. The plastic I used was Kel-F, which is a hard relative of Teflon with a melting point much higher than normal plastics; it is routinely used on pressure fittings exceeding 20,000 psi.

Test Firing:

I decided to lube the buckshot to hopefully reduce leading of the barrel. I took a plastic cup and shook up some buckshot with liquid Alox (Lee Industries) and let it dry. It forms a thin coating of Alox on the surface but does not affect the handling or loading of the pellet. The first shot was with a full load (a whole four grains of Swiss 4F), with a long string tied to the trigger and me behind a tree. The gun made a satisfying little “whap” and emitted a tiny puff of smoke, and that was all there was to it. There was little gas blow-back, and no evidence of any mechanical stresses. The next shots were taken by hand, shooting through a chronograph.

Goex Clear Shot 2F – 710 fps (Not as fast as my pellet gun)

Swiss BP 3F – 1118 fps

Swiss BP 4F – 1182 fps

Then I advanced the bolt a bit to slightly compress the powder:

Swiss BP 4F – 1350 fps – More like it!

With 2 grains Swiss 4F -

Since I only had 2F in the Clear Shot, I pulverized some, but it generally wouldn't go off, since only the outer layer is graphited and therefore conductive (the inside is a funny brown color and not electrically conductive). On the one shot where it went off, it chronographed at 1100 fps. As expected, the black powder worked best, but it fouled more slightly than the Clear Shot.

The rifle worked well for the first 50 shots or so, but then I noticed more and more fouling build-up in back of the chamber. Looking at the plug under magnification showed that the gasses were channeling around the plastic and eroding little gullies in it (Figure x). In fact, some of the plastic was being evaporated from the sides of the plug and deposited in the action – talk about sticky residue! It was clear that another approach was needed.

Version #2 of the breech plug was built with a thin walled stainless steel cup at the end (Figure xx). The wall was cut with a two degree taper, annealed at the end and slightly flared so it made a loose friction fit with the chamber. This way, the gas pressure acted to force the walls of the cup against the chamber, providing a tight gas seal. With this arrangement, fouling of the bolt and chamber was much reduced, and there is no evidence of gas channeling.Because the walls of the cup were annealed and flex less than 0.001 inches, cracking should not occur in the forseeable future. The plastic insulating cup is no longer exposed to gas erosion, so it too should last for a while; the temperatures in the firing chamber are high, but too transient to do more than glaze its surface.

Performance:

So, after all of this work, how well does it shoot? It is indeed fun to shoot, and if I keep the load down to two grains of Swiss 4F, it goes off with a little 'pop'. If it is loaded up to four grains, it sounds like a normal .22 long rifle. As to accuracy, I'm still not sure. It will hold a 'minute of tin can' at fifty yards, and at 25 yards, the tree rats don't have a chance.

The cost of shooting is tiny:

#4 Buckshot (bought in 5# bag) - $0.008

Powder (2/4grains) - $0.006/$0.012

About 2 cents/shot at maximum load - quite a lot of bang for the buck!

You can also use 32 grain .22 short slugs (ordered from North American Arms), or .22 pellets (Crossman Premier)

Cleaning is a breeze; the barrel detaches from the stock just like the original Ruger 10-22, and after removing the receiver cap, the bolt is pulled out of the receiver. The barrel can then be flushed with water, and the tip of the igniter bolt scrubbed down with a toothbrush. The whole operation takes less than five minutes, and since everything is stainless steel, rusting is never an issue.

Waiver of rights:

The material presented here may be used by any person or organization for either personal or commercial use without any payment to the author of any kind. No patents have been applied for, nor does the author intend any commercialization of this work. If some party wishes to commercialize any or all of this material, they have my blessings.

Stephen Wardlaw

2004-04-20T09:31:49