Because if Cracked Magazine is anything, they're scientific!

"So their premise that fully automatic shooting only takes place in a matter of 4 seconds is bullshit. "
Technically the example they gave (the commando reference) it's a clip fed weapon, not belt fed, thus "4 second" example applies. Also, there's a reason why the 249 and M60, 50 cal etc have replaceable barrels, over time the barrel can bend due to high constant rate of fire.

Jesus, gun fanatics get so uptight..