The exists in a legal twilight zone. It is simultaneously a piece of irreverent gun culture satire and a potential federal felony waiting to happen.
The following article explores the history, mechanical function, and severe legal risks associated with these devices. What is a Drop-In Auto Sear (DIAS)? Drop In Auto Sear Keychain
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. The exists in a legal twilight zone