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