Thursday, May 30, 2019

Janelle gets a bee in her bonnet



Janelle sat, staring at the table covered with the parts of a disassembled rifle.

Kelly was not the kind of man to fill the air with senseless chatter. He let her stare.

After five days of watching her spend virtually every spare moment just staring at the parts, Kelly caved.

“What are you thinking?” he asked.

“I am thinking the shotguns were a piece of cake.” Janelle said. “I think it is time to reach a little bit.”

They agreed to build the shotguns in “batches” of ten. That would give them some efficiencies of scale but would also give them opportunities to make changes.

The first batch was a struggle. The second batch of ten was hard. The next two were built with no issues. Even though they had planned on building 100, the demand slacked off after thirty-five. They they stopped building at fifty preferring to conserve resources. The fifteen extras were in the vault.

Kelly got a cold chill down his spine. Janelle was looking at a disassembled AR-15, a very sophisticated weapon that used high-tech processes.

“You aren’t thinking of making AR-15s, are you?” Kelly asked.

“Nope.” Janelle said.

Kelly’s relief was short-lived.

“We are going to have to make a lot of changes if they are going to work with black powder.” Janelle said.

That is when the hackles went up on the back of Kelly’s neck.

A bit of history is in order to make sense of what Janelle said.

The AR-15 was a space-aged weapon made from forged, aircraft grade aluminum and made with exquisitely tight tolerances.

When first deployed in Vietnam, the weapon was subject to jamming after relatively few rounds were fired. The cause of the problem was quickly traced to the chemicals added to the smokeless powder to buffer the acid products that accelerate the deterioration of smokeless powder in hot, humid climates.

The other factor that made the AR-15 exquisitely sensitive to powder residue is that the design is a “direct impingment” design. A small hole was drilled in the barrel and a tube carried the high pressure, contaminated, gasses directly into the upper receiver where a small piston/cylinder arrangement harvested the energy of the gasses…and then indiscriminately spewed the ash contamination into the upper receiver where all the small, moving, closely fitted parts lived.

Other chemical buffers were found that did not leave solid residues and the problem, mostly, went away.

Approximately 1% of the original smokeless powder became solid residue that gummed up the lockworks. By contrast, black powder leaves almost 50% of its original mass as solid residue.

Had it been anybody other than Janelle, Kelly would have harshly rebuked them for the stupidity of the idea.

“Why black powder?” he asked.

“Someday we are going to run out of components for reloading AR ammo. I am trying to stay ahead of the game.” Janelle said.

“You know that you picked about the worst action in the world for running black powder, don’t you?” Kelly said.

“Yup. That is why it has to be changed.” Janelle agreed as if that was not a big deal.

Poking the gas key on the bolt carrier, “Why does that have to be in the upper receiver?” Janelle asked. “Why can’t the gas key be longer and have the gas tube end in the hand-guard?”

Kelly had never thought about that.

“And since the gas is still under pressure when the gas key moves away from the gas tube, why not cut the end of the gas tube on the diagonal so it biases the gas to the right and out of the handguard or route it around and vent it out the bottom?” Janelle asked.

“Those guys who build two-stroke racing motorcycles know a lot about using pressure and momentum to move air and fuel where they want it.” Janelle said. “I don’t see why we can’t use tuning to kick most of the gas out, away from the upper receiver and action.”

“You know black powder cartridges won’t have nearly the power of smokeless ones, right?” Kelly asked.

“Yeah, I get that. But everybody else will be running out of smokeless powder ammo. too.” Janelle said. “It is like the old joke, I don’t have to be able to out-run the grizzly bear. I just need to be able to out-run the guy I am fishing with.”

“I looked up the ballistics of the old 25-20 Winchester. It has a case volume similar to the 5.56mm round.” Janelle said. “1500 feet per second for an 85 grain bullet is a lot more impressive than a .22LR pushing a 40 grain bullet at 1200 feet per second.”


"The other thing I was thinking was to see how much potassium nitrate we could replace with ammonium nitrate. Ammonium nitrate won't leave the residue that saltpeter does." Janelle said.

“So what are you going to do about receivers?” Kelly asked. “It is not like we have a forging press for 7075 aluminum.”

“You are right. We don’t.” Janelle said. “The lower receivers don’t need to be that good. Heck, you can buy them...” then she corrected herself “...you used to be able to buy them made of polymers.”

“Did you know that we have a neighbor who worked in a small shop making investment castings for a company that sold custom jewlery?” Janelle asked.

“You mean Bob?” Kelly asked.

“Yeah, Bob.” Janelle said. “I bet Bob could design and make the patterns in his sleep.”

“I thought investment casting used wax pieces that were melted out of the mold.” Kelly said. “Why would we need molds?

“I was thinking it would be more ‘production’ if we used steel molds for the exterior surfaces and sand or plaster cores interior surfaces that aren’t undercut. Then use Bob’s wax pieces for the most detailed areas.” Janelle said.

“I still don’t think you will be able to hold the tolerances the AR demands.” Kelly said.

“That is what shims are for.” Janelle said.

Next

7 comments:

  1. The other issue with early AR rifles was the timing of the pressure curve due to the burn rate of the powder. This is a big deal in many gas operated rifles. The 5.56 ammo powder was changed from the original spec, which caused the pressure inside the chamber to still be too high for extraction when the bolt began to move, which, along with the chamber corrosion issues, led to extraction issues.

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  2. There are reasons that nobody, as far as I know, has ever made a black powder semi-auto - not just the fouling, but the burn curve as B mentioned, and the lack of power.
    If you are looking at a weapon for black powder or even early smokeless/ cordite powders, a far better idea would be a pump or level action. And while the 25-20 may have been fast for a black powder round, most black powder rounds use BIG bullets to make up for the slow speeds from black powder.

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    1. Maybe I am reading more into the snippets I read but was of the understanding that infantry weapons were sized with the intention of being able to disable or kill a horse at 600 yards. Horses are much better targets than a man in a foxhole.

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  3. Gotta agree with B and Johnathan. That dog won't hunt in black powder, in addition to being overly complicated for a 'homemade' weapon. Shims MOVE... Always... sigh

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  4. I did a little half assed research into ammonium nitrate powders a few years back. In the late 19th and early 20th century a blend of AN and carbon was used under the name of Amidpulver and Amonpulver. It was equivalent in power to double base smokeless powders of the time, but it was flashless because it completely burned in the barrel. It took a hotter primer to ignite it but once lit it burned cooler. It was hygroscopic, but the biggest problem was it had a crystalline phase change at 32.3 C (90.14 F). In the summer when temperatures would frequently go back and forth over 90 the crystals changing shape would cause the pellets to crumble, changing the burn rates. I did wonder if instead of adding carbon you could encapsulate the AN in something that would hold it together, keep the humidity out and serve as fuel like cellulose acetate but I never found a way to test it.

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  5. The Browning 'Potato Digger' machine gun ran FULL automatic with black powder. While I don't see that swinging arm as practical for an individual weapon, the gas system of the Ruger Mini 14 and Mini 30 is kind of similar. Make it a cruciform fitting with one to the gas port, 90 degrees to that the fixed piston and the other two captive clean out fittings to make cleaning the gas system easy and it ought to work.
    ISTR that black powder bores smaller than 8mm or .32 foul up very fast, if that is true you might want to work your design around 7.62 x 39 or 300 Blackout.

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  6. When I went shooting for the first time (with an AR) with The Boy, I tossed him the AR and a cleaning kit and said, "clean this."

    He did. It took him two hours and several YouTube videos, but he did.

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