My experience with firing a SAW from the standing position is very limited – like one time limited. And even when everything goes completely right, the adrenaline rush of squeezing off bursts from a light machine gun while compensating for gravity and inertia can be hair-raising.
The video below shows what can happen when normal operations start to go bad quickly. From the looks of it, the rear take down pin from the trigger assembly walked out, separating the gun from the shooters grip. The front pin remains in place while the gun appears to finish off its last remaining rounds, all the while pivoting towards the soldier. Yowzah.
In reality, the assistant gunner was quick enough to break the links on the belt and prevent the impending disaster.
On the M249, the sear is in the trigger assembly, meaning that in the absence of the assembly itself, the machine gun is free to run as long as the ammo keeps flowing.
Luckily, it appears everyone walked away unscathed. A few more links on the belt and this would have been a very bad day.
Full SAW video here:
TFB’s Miles V. sent me this additional video of another runaway M249. He adds:
Belt-fed machine guns require a different approach to safely operating and maintaining them in the Infantry. As an example, whether an M249 SAW, or a M240B, both are considered “Area Fire” weapons as opposed to a “Point Fire” weapon such as the M4 or M16A4 (out to a certain distance, after which they too become an “Area Fire” weapon system). Another point is that the M249 SAW doctrinally cannot be used to initiate an ambush, or enter a room in a MOUT scenario. This is because of the open bolt operating feature and the possibility of a malfunction on the first round. Similar principles exist with safety. Clearing a belt-fed requires the user to point his head down, thus exposing only his kevlar helmet to the chamber while at the same time popping the feed tray cover, also while holding the bolt to the rear.
The example of the M249 SAW in this video having the trigger group come clean off because of a faulty retaining pin creates a situation known as a “Run Away Gun”, wherein there is nothing to stop the bolt from cycling rounds from the belt on fully automatic. More commonly this happens when the sear is broken or otherwise inoperative and doesn’t involve the entire trigger assembly coming off. Standard operating procedure for this malfunction is to keep firm control of the machine gun, while pointing it in a safe direction downrange, allowing the rounds to continually fire. If the belt being used is under 50 rounds or so, the gunner just needs to let the gun run its course through the entire belt. If the belt is over 50 rounds, it is the responsibility of the gunner on an M249 SAW to either “break” the belt by quickly disconnecting the links, or to actually twist the belt into a position wherein the gunner has essentially caused an intentional malfunction, by not allowing proper travel of the belt into the feed tray entrance.