The NYTimes.com has published two videos recorded by Colt Defense. They compare the M4 and the M4A1.

M4 Barrel bursts after 535 rounds.

M4A1 still going after 911 rounds (although gas tube melts preventing semi or full auto fire)

The NYTimes reports …

That video shows the same test with an M-4 equipped with a thicker, heavier barrel, which is used on a specialized carbine, known as the M-4A1. This variant is carried by some Special Operations users.

…

Colt Defense and the Army have been discussing making the change to a heavier barrel for several months and appear likely to begin requiring standard-issue rifles to have the barrel previously manufactured for the M-4A1.

Sounds like Colt is going on the PR offensive.

[ Many thanks to all the readers who emailed in these videos. ]