Tag Archives: Laws & Rules

The fix is in: proposed rulemaking on bump-fire

The ATF has posted a PDF document which will officially be published December 26, 2017. It solicits comments on proposed rules on the “Application of the Definition of Machinegun to “Bump Fire” Stocks and Other Similar Devices.”

The document makes it clear that bump-fire stocks (and other devices) will be classified as machineguns under the NFA definition. It is troublesome in other ways, as well.

“‘Bump fire’ stocks (bump stocks) are devices used with a semiautomatic firearm to increase the firearm’s cyclic firing rate to mimic nearly continuous automatic fire.”

They absolutely in no way affect the firearm’s cyclic firing rate; it’s impossible:

The rate of fire of a semiautomatic firearm is based in physics. Force is applied to the firing pin. That force and the pin’s mass determine it’s acceleration into the cartridge primer. The primer ignites at a given velocity for that cartridge; that in turn ignites the powder with its own ignition velocity. The bullet is propelled forward; force and mass again.

The force of the detonating powder also works to move the bolt backwards; the old “equal and opposite reaction.” How fast the bolt goes back is determined by its mass and the resistance of the spring behind it. When it has traveled all the way back, the spring applies force and pushes the mass forward once again.

The bolt is slowed as it strips the next round out of the magazine. Finally it moves the round’s mass into the chamber.

In a machine gun, the firing pin would continue forward starting the cycle over again. In a semiautomatic firearm, the pin does not go forward until the trigger (with its own mass and springs) returns to the ready position and is manually operated again. So semiautomatics have an inherently slower rate of fire than machine guns, all else being equal.

The only way to even approach the theoretical maximum rate of fire of most semiautomatics is to have a fast finger.

Instead of looking at mechanical function, and simple physics, in this document the ATF has adopted the media and gun controller definition of “if it’s fast, it must be a machinegun.” The intent is preordained regardless of comments.

As I have explained, bump-fire stocks are training wheels, and no more make a semiautomatic rifle work as a machinegun than training wheels turn your child’s bike into a high performance racing machine.

Next, we have another problem.

“On October 1, 2017, 58 people were killed and several hundred were wounded in Las Vegas, Nevada, by a shooter firing one or more AR-type rifles affixed with a particular bump stock device.”

How does Deputy Director Thomas E. Brandon know that? Is he privy to data from the investigation which has not been released to the public? Or is he assuming the media claims (not investigator statements) to that effect are true?

In no news story I can find is there a statement from authorities of what weapons were used. We were told that there were 23 weapons in the asshole’s suite, that some were AR pattern semiautomatic rifles, that at least one was an AK pattern semiautomatic rifle, that weapons were chambered in 5.56/.223 and .308, and that at least one rifle in addition was fully automatic. But not which were actually used.

If the bump-fire stocked rifles were used, as this document states, why won’t investigators say so? If it was being kept confidential for legitimate investigative purposes, why release the data in this very public document?

A law enforcement source has said that the shooter left behind a note with ballistic calculations “pertaining to the distance and trajectory from his 32nd-floor window to the crowd of concertgoers he targeted below.” Such calculations are pointless for inherently inaccurate bump-fired rifles: “What’s the point of careful calculations of the most accurate way to aim a firehose? An automatic rifle in most people’s hands wouldn’t be much better.” This suggests that the plan was certainly to use something other than bump-fire.*

In preparing for new bump-fire stock rules, the ATF starts with the unsupported claims that such were used in Las Vegas, that they magically change the physics of a firearm’s internal action, and operating the trigger rapidly makes them work like machineguns. So does your well-trained finger.

The fix is in.


* It also raises questions on the need for precise ballistics calculations when we’re told the “target” was simply 22,000 random people crowded into an area the size of multiple football fields, and why he stopped shooting.


Carl is an unpaid TZP volunteer. If you found this post useful, please consider dropping something in his tip jar.

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