Public Service Announcment: check for fire-on-release triggers

[Texas_Mike]

Typically, on a new rifle that malfunctions and fires upon release of the trigger, it is due to an incorrectly installed disconnect spring, and less common, from out-of-spec lower parts. With the trigger at the rest position, and the hammer pushed back until the sears are at their closest position, there should be a gap between 0.001" to 0.003", no more. If the distance is greater, and the lower parts are within verified tolerances, than an out-of-spec receiver with poor pin hole placement is considered as the culprit. If this is the case, then replacing lower parts may temporarily alleviate the symptoms of this issue, but the malfunction will ultimately return. Measuring these components and verifying critical dimensions, as well as verifying that they are within specification by evaluating their functional relationship with one another, is important when attempting to troubleshoot an issue like this.

[Ned Christiansen]

M-16. If you have the auto sear, which can be detected from the exterior by the presence of the auto sear pin over the selector, or if the receiver has the pin hole and will accept an auto sear, even if it’s a stripped receiver with no parts in it whatsoever, it’s a machinegun. A selector that rotates 180 from "safe" as shown in the pic could be a hint that something's different. In a standard semi-auto set-up the selector is prevented from going to that position.


Auto parts on right, semi-auto parts on left. Note the “busy” selector—it has a few more features because it has a few more functions. Notice the hook at the top of the hammer, the long-tailed disconnector, and the open-backed trigger to make room for the disconnector’s long tail. My opinion, my advice, would be, “don’t have any of these in your semi-auto AR-15". Again I’m no expert on the regs and this is not genuine legal advice. Just saying, if it’s not papered as a machinegun, it would seem a good idea not to have any machinegun parts in it, although an M-16-style carrier alone, is specifically allowed.


Semi-auto trigger and disconnector left; auto parts right. Again note on the auto parts, the disconnector’s long tail and how the open back of the trigger allows it to fit in place. On the semi-only parts, the disconnector tail is shortened so a select-fire selector cannot act on it, and the wall at the trigger body’s rear prevents the installation of a long-tailed, select-fire disconnector.

[Ned Christiansen]

This is pretty good too, I don't know the source: