The first video shows an M-4 being subjected to an intensive sustained-firing test. The rifle used is the standard M-4 with a standard barrel. The weapon is secured on a bench and fed one full 30-round magazine after another without rest beyond the time it takes to replace empty magazines with full magazines.I've seen M16s and M4s go red hot during sustained firing at Knob Creek, and I've seen AR barrels twist like pretzels when thrust red hot into cold water, but I've never seen a barrel rupture like the test barrel in the first video.
Watch the video closely. After several magazines, the barrel smolders. Then it becomes red hot. After 1 minute and 20 seconds the barrel begins to droop between magazines — like a piece of warm licorice. Then comes the catastrophic ending, at 1 minute and 51 seconds and after the 535th round, when the barrel ruptures.
It is worth noting that the test simulates conditions that almost no soldier could face. In it, 18 magazines are fed through the rifle in less than two minutes. Soldiers and Marines armed with an M-4 or M-16 (the carbine’s longer-barreled parent) typically carry seven or so magazines.
Not to defend the M4, but I do wonder if it's possible to build anything short of a squad automatic weapon that can stand up to sustained full auto fire. Obviously in the Colt tests the heavy barrel held up better, but it didn't make 1000 rounds either. I would rather see the military closely studying the results from competitions like Dave Lauck's hellish ITRC, where the carbine shooters can expect to run 1000+ rounds through their guns under as close to real world conditions as Dave and his military buddies can tinker together — an event designed to stress the guns to the max. There is a ton to be learned watching guns fail under these "lab" conditions!
As we said when we did the torture test on the Para 1911 a couple of years back, heat is the natural enemy of all metal, and we know how to generate a lot of heat.