a hand held weapon capable of about 12 rounds a second? What are you drinking. Damn gun would melt.
One assumes that there is sufficient ammo in a belt-feed situation. The site below says 700 to 950 Rnds/min.
http://www.globalsecurity.org/military/systems/ground/m4-specs.htm
But yes, the M4 isn’t built to handle sustained fire rates like that. It’s a burst weapon at best and with a 30 rnd mag, (100, if you get one of those poly ones, which from what I’ve read don’t work especially well).
I would think that after one 700 round minute that the whole weapon would be liquid.