Infinite Capacity - Surgical Accuracy: The M240 SLR from Ohio Ordnance Works, Inc.
I was speaking of this !
The M249 has a distinct sound and fires at 800 to 1000rpm way faster than the audio from that attack!
The old ones were 650-850 rpm, but when they did away with the adjustable gas regulator, they were factory set at 650. I actually thought the cadence was pretty close to a 240. But a 240 is very regular, like a sewing machine. But some folks don't press the trigger like they are supposed to, and the sear catches occasionally.
I kind of thought the supersonic crack was too high pitched to be 7.62, and sounded a lot like being down range of 5.56, but that was on crappy cell phone audio.