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 considerably before the ball begins to move. I decided to use #4 buckshot, which is .240 inches diameter (20.7 grains), in a 0.250 inch 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.
These tests did point to another method; in performing the experiments, I had measured the resistance of a
lightly packed pile of 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 the energy is dissipated as heat. The formula for this
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 trigger mechanism acted as a simple switch to connect the power supply to the igniter plug via a contactor in the bed of the stock.
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.
The left view is a close-up of the barrel bed, showing the spring-loaded contact from the power supply and a small adjacent spring which forms the ground contact. As seen on the right, when the bolt is fully closed, the bolt contact aligns with the bed contact, allowing the rifle to fire.
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, but 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 here in the schematic drawings of the action; there is also a 'pdf' you can download here. 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.
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 'Pow' 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!
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 slightly more than the Clear Shot.
To cut down the noise, I reduced the powder charge to two grains and tried several different projectiles. All
shots were taken at 50 yds.
|Load ->||Buckshot + Alox||Plain Buckshot||Crossman Pellets*||Beeman Pellets**|
|Std. Dev. Vel.||42||31||38||23|
* Crossman 'Premier' 14.3 grains, unlubed. They look like little Minie balls.
** Beeman 'Silver Arrow' pellets.
*** Not on paper (The target paper was 18" square!)
I fired a round from a clean barrel into a water trap to see what happened to the ball as it was swaged into the rifling. A second round was retrieved after firing it through a barrel fouled by about 20 shots. The picture below shows how the ball swaged into the clean barrel has a smooth surface and crisp rifling marks, but the ball fired through the fouled barrel looks pretty crummy. It is surprising that the rifle groups as well as it does, considering the beating the ball takes in the fouled barrel. I repeated this with the Crossman pellets, and the results were similar, although the pellet was in much better shape; the skirts were worn more on the fouled shot, but the head of the pellet was fairly good. This may be why the pellet groups better than the ball.<
Some Alterations Required...
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. 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.
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.
So, after all of this work, how well does it work? 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), as well as the Crossman Premier .22 pellets.
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 not an issue.
I have now used the rifle for about three months; several times a week I go out onto our deck in the evenings and burn up a pan-charger full of powder, two grains at a time. Reactive targets are set up; a one inch 'swinger' at 10 yards, a 6" 'bird' at 50 yards and my favorite, a cut-off propane cylinder (hand torch type) gong at about 35 yards. If the light is good, I can hit them most of the time, although when the barrel fouls, the 50-yard target is very iffy. When I think the accuracy is falling off, I squirt a little water down the barrel to soften the fouling, place a small wad of paper toweling through the breech to dry the chamber and load as usual, firing the mess in a direction that won't spatter the house [Don't cringe - there are only two grains of powder in there]. This 'field cleaning' seems to restore the accuracy fairly well. All in all, it is a lot of fun to shoot, and I am very glad I made it.
Follow Up #2 - Still Not Perfect...
After a couple of hundred shots, the gun would no longer fire. It turned out there was some gas-channeling through the plastic, between the igniter and the bolt, which carried carbon and other black powder salts with it. When even the slightest bit damp, this conducted the electric charge away from the powder, preventing ignition. I changed the design to a small mushroom-shaped igniter in a larger Kel-F plastic body using a strong press-fit. The theory was the pressure from the powder gas would force the head of the 'mushroom' down into the plastic, helping to keep a seal.
Oops... After another few hundred shots, the igniter button literally fell out. Gas had channeled around the mushroom and eroded a good bit of the plastic. This was a good test of the safety factors discussed earlier; although a good part of the powder gas was going backwards, its force was completely dissipated and not even noticed by the shooter. The pictures below show the remains of the igniter assembly.
So - Igniter version #4 was constructed with a slightly different design philosophy. This time, a more flexible plastic, Nylon-66, was used in place of the Kel-F in the hope of effecting a tighter gas seal. The 0.204" nylon plug was force fit into the 0.200" cup. A 0.104" stainless steel igniter pin was then force fit into a 0.200" deep, 0.101" diameter hole drilled into the plug. As you can see from the oversize, there was quite a lot of force fitting involved; in fact, the OD of the breech plug increased from 0.250" to 0.254" and had to be re-dimensioned. Since the force on a 0.104" pin at a 10,000 psi chamber pressure is only about 80 pounds, it was hoped everything would stay in place. A dozen test shots later everything was still intact; a follow-up report will be posted as things develop...
Follow Up #3: Perfection - and Obsolesence...
After a few hundred shots, the plastic insulator was again eroded through, so I did what I should have done the first time - I used ceramic. Fused alumina has a compression strength of around 180,000 psi - close to that of high-strength steel. It does not have much shear resistance, but since it would be mounted inside a steel shell, that didn't really matter. I used a 0.200" fused alumina rod, drilled for a 1.5mm electrode, which was then swaged into a 0.199" hole in the end of a 0.250" stainless steel rod to form the igniter. Finally, this worked perfectly with no gas leakage or erosion after many hundreds of shots.
However, the success of the igniter started me thinking of another project; a similar rifle but one which could use smokeless powder. That design can be seen to the right, and my once proud little smoker now sits all alone in the corner with no one to play with - such is life... If you click on the picture, you will see the new toy.
Where to go next - in no particular order...
- Fit a larger caliber barrel.
- Find out how to directly ignite Pyroxex, etc (Not using a duplex load.)
- Develop an igniter as a percussion cap replacement (Electric drum?).
But Is It Traditional?
I can't claim that this is a traditional design, but then again, the technology to make a rifle like this was known in the late 18th century. No examples of such a weapon have ever been found, but perhaps some crazed inventor made one in his basement to see if it could be done - just like me!