Commenting Now Open: Application of the Definition of Machinegun to “Bump Fire” Stocks and Other Similar Devices.

As mentioned last week, the ATF has proposed a rule which would render bump-fire stocks, and trigger assist devices, “machineguns.”

The Zelman Partisans opposed this when legislation was introduced to do the same thing, and we opposed doing it via bureaucratic fiat.

Comments are now being accepted on “Application of the Definition of Machinegun to “Bump Fire” Stocks and Other Similar Devices.” You may submit comments online through the Federal eRulemaking Portal.

I have submitted my personal comments already. This what I sent.

Bureau of Alcohol, Tobacco, Firearms, and Explosives
Docket No. 2017R-22

I oppose classifying as machineguns “bump-fire” stocks or any other external device or accessory which does not alter the internal action of a firearm.

In effect, this proposed rule would make any firearm a machinegun if a well trained person can pull the trigger faster than your arbitrary threshold.


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 its 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.

A machinegun is designed to fire multiple rounds per trigger operation. Bump-fire stocks in no way affect that operation/rounds relationship. If you put a bump-fire stock on a semiautomatic rifle, you still individually operate the trigger for each round fired. Bump-fire stocks do not make the weapon fire faster. The theoretical rate of fire of the rifle is determined by the physics of the internal parts, as described above.

To fire a rifle with reasonable expectation that the round will hit the target, you normally hold the rifle firmly with both hands, and pull it against your shoulder. This provides a stable shooting stance.

A rifle has recoil. When fired, it pushes against your shoulder.

But let’s trying hold that rifle a little differently. With your off hand (the hand you don’t use to pull the trigger) grip the rifle. Your trigger hand does not grip the rifle. Nor do you pull the rifle butt snug against your shoulder. It isn’t a stable stance, and accuracy will suffer.

When your rifle is on target, extend your trigger finger into the guard. Now, with your off hand grip, push the rifle forward until your trigger finger pulls the trigger.

The rifle fires. Recoil pushes the rifle back so your finger disengages the trigger. Your rifle-gripping off hand acts like a spring and pulls the rifle forward again. If your shooting finger was held steady, the trigger is pushed against the finger again, firing.

The bump-fire stock is simply a device that can be pulled snugly to the shoulder, and provides a grip to help keep the trigger finger in position. The rifle proper just recoils back in a channel into the stock. It is training wheels for folks who have trouble bump-firing. And since it’s a bit more stable, it helps with accuracy compared to normal bump-fire. However, accuracy even with the stock is poor compared to conventional stance with conventional stock.

Considering bump-fire stocks, and other accessories, to be machineguns would not simply regulate a physical device. It effectively outlaws the bump-fire TECHNIQUE, and even pulling the trigger faster than some arbitrary threshold.


5 thoughts on “Commenting Now Open: Application of the Definition of Machinegun to “Bump Fire” Stocks and Other Similar Devices.”

  1. Carl… do you actually think any rational explanation of anything will influence the bureaucrats? Do you think that any of them CARE in the least? If they were the least influenced by reality, none of this would be happening.

    Evil is not reversed by careful explanations. The desire/compulsion to control the lives and property of others is the ROOT of all evil.

  2. Well said, clearly expressed position. But it is not what the Feds are looking for… From the ATF posted request for Comments:
    ATF requests comments on this ANPRM from all interested persons with information about the enumerated questions. ATF specifically requests comments on the questions listed above, on the costs or benefits of the proposal in this ANPRM, and on the appropriate methodology and data for calculating those costs and benefits.


    21. In your experience, where have you seen these devices for sale and which of these has been the most common outlet from which consumers have purchased these devices (e.g., brick and mortar retail stores; online vendors; gun shows or similar events; or private sales between individuals)?

    22. Based on your experience or observations, what is (or has been) the price range for these devices?

    23. For what purposes are the bump stock devices used or advertised?

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