Suppose there is a device that repeatedly pulls the trigger of a semiautomatic firearm, effectively allowing it to fire repeatedly without any repeating manual action. What laws, if any, restrict the use and sale of this device?

I'm interested in answers for any jurisdiction, but particularly for US federal law and individual states.

  • 3
    Such as a tripwire? I hope your booby trap can distinguish friend from foe (and from you). Commented Mar 19 at 20:14
  • @WeatherVane no, I was thinking of something that someone would manually activate. The idea is similar to a bump stock: a way to simulate a fully automatic firearm while possibly avoiding legal issues. I'm not planning to actually do this; I'm just curious what laws would apply.
    – Someone
    Commented Mar 19 at 20:26
  • I should have made the question clearer; by "without any manual action" I meant "without any repeating manual action."
    – Someone
    Commented Mar 19 at 20:30
  • 1
    The device is often called a "bump stock" and this is the subject of currently pending SCOTUS litigation. These were classified as machine guns during the Trump Administration by the federal government, which effectively banned them. That has been challenged now.
    – ohwilleke
    Commented Mar 19 at 20:36
  • So you want to know if it is legal to convert your weapon into an illegal weapon? Commented Mar 19 at 21:27

3 Answers 3


This will potentially be decided by the Supreme Court of the United States in Garland v. Cargill.

The issue in Cargill is whether a bump stock device constitues a device "designed and intended, for use in converting a weapon into a machinegun" — a machinegun being a weapon which shoots "automatically more than one shot... by a single function of the trigger."

If so, bump stock devices would be regulated as a machinegun under 26 U.S.C. § 5845(b).

As is apparent from the written and oral argument, the terms especially in dispute are:

  • "single function,"
  • "trigger," and
  • "automatically."

When the Supreme Court gives meaning to the various terms in 5845(b), we will then be in a position to answer your question.


That would be a machine gun. Regulations would prohibit civilian ownership if it was constructed after mid-1986. Transfers of devices predating must be licensed by the ATF.

A machine gun is defined as

Any weapon which shoots, is designed to shoot, or can be readily restored to shoot, automatically more than one shot without manual reloading, by a single function of the trigger...


Any part designed and intended solely and exclusively or combination of parts designed and intended for use in converting a weapon into a machinegun, or...

Since you have explicitly stated "without any manual action," it would be clearly a machine gun.

Bump stocks have yet to be banned because it requires multiple "functioning of the trigger". There are other gray area devices, like trigger cranks.


If the device makes the gun repeatedly fire in response to a single human action, it and/or the combination of it and a gun would almost certainly be considered a machine gun by the ATF.

The action that initiates this device would then be considered a new trigger.

See this article in which the ATF "determined" that an electromechanical trigger-pulling glove qualified as a machine gun. Note that the maker of the glove believed that the the glove required the user to move their finger at least a little, but the ATF claimed that this was not neccessary.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .