You may have seen this story hitting the press about the M4 and M249 machine guns
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Looks like the story is mostly about over heating of the weapons.
"Do U.S. armed forces have the best guns money can buy?"
"Despite the military's insistence that they do, a small but vocal number of troops in Afghanistan and Iraq has complained that the standard-issue M4 rifles need too much maintenance and jam at the worst possible times."
<broken link removed>
Looks like the story is mostly about over heating of the weapons.
"Do U.S. armed forces have the best guns money can buy?"
"Despite the military's insistence that they do, a small but vocal number of troops in Afghanistan and Iraq has complained that the standard-issue M4 rifles need too much maintenance and jam at the worst possible times."