The "I didn’t know" defense doesn’t work. The "It’s on a keychain" defense doesn’t work. Multiple individuals have been prosecuted for possessing DIAS keychains. In one notable 2019 case, a man was arrested at a gun show for selling "novelty" auto sears attached to keyrings. His argument that they were "just key fobs" was rejected by a federal judge when prosecutors demonstrated they could be installed into a rifle with minor fitting.
In ATF Ruling 81-4, the agency made clear that a device is a "machine gun" if it was originally designed as a fire control component. Adding a secondary function (like a key ring holder) does not negate that primary design. In plain English: Drop In Auto Sear Keychain
Typically, these are one of three things: The "I didn’t know" defense doesn’t work
The device works by interacting with the bolt carrier group and the trigger assembly. In one notable 2019 case, a man was
In a standard semi-automatic AR-15, the trigger must be pulled for every shot fired. A true military M16 uses an internal part called an to hold the hammer back until the bolt is fully closed, allowing for continuous fire.