The Ground Precautionary Message ACALA #97-031, from November 2006, clearly states that if an M4 barrel reaches just 737 degrees Celcius, the barrel will be weaked to the point where burst.
(3) BURST BARRELS RESULT WHEN THE WEAPONS ARE FIRED UNDER VERY EXTREME FIRING SCHEDULES AND THE BARREL TEMPERATURE EXCEEDS 1360 DEGREES FAHRENHEIT. WHEN THE BARREL REACHES THESE EXTREME TEMPERATURES, THE BARREL STEEL WEAKENS TO THE POINT THAT THE HIGH PRESSURE GASES BURST THROUGH THE SIDE OF THE BARREL APPROXIMATELY 4 INCHES IN FRONT OF THE CHAMBER. THIS CONDITION CAN RESULT IN SERIOUS INJURY.
You are not going to see an M4 barrel white hot because by that point it would have exploded!
The AP also infers that the M4 Carbine is designed to handle a high rate of fire
The high rate of fire appears to have put a number of weapons out of commission, even though the guns are tested and built to operate in extreme conditions.
This is also not true. From the Ground Precautionary Message[^1]:
(B) FIRING 140 ROUNDS, RAPIDLY AND CONTINUOUSLY, WILL RAISE THE TEMPERATURE OF THE BARREL TO THE COOK-OFF POINT. AT THIS TEMPERATURE, ANY LIVE ROUND REMAINING IN THE CHAMBER FOR ANY REASON MAY COOK-OFF (DETONATE) IN AS SHORT A PERIOD AS 10 SECONDS.
(D) SUSTAINED RATE OF FIRE FOR THE M16 SERIES RIFLES AND M4 SERIES CARBINES IS 12-15 ROUNDS PER MINUTE. THIS IS THE ACTUAL RATE OF FIRE THAT A WEAPON CAN CONTINUE TO BE FIRED FOR AN Indefinite LENGTH OF TIME WITHOUT SERIOUS OVERHEATING.
I've gotta say, this crap is not encouraging my confidence in this weapon for the troops.