Every since it was introduced, the M-16 has been dogged by reports of jamming at the wrong moment. Now it spin-off carbine is facing the same issue of jamming. The military has stressed better cleaning and maintenance as a way to reduce stoppages--although enemy forces rarely give our forces a time-out so they can clean their weapons. In a 2007 test, which compared the M-4 to three other carbines, the M-4 came in last in terms of reliability. In the test, ten weapons of each type fired 60,000 round under real-world conditions. The M-4 had 882 stoppages, compared to 233 for its nearest competitor (nearly four times the failure rate). To put this in context, a soldier with a combat load of 3 thirty-round magazines can expect a stoppage before running out of ammo (under ideal conditions). Of the stoppages, 19 required an armorer to repair, meaning the average weapon was twice rendered useless during the course of the test. The reason for the stoppages is primarily because of the direct impingment gas-operated action. In this system, gas from the fired round is forced through a narrow tube, working the action of the weapon. The advantage is that it minimizes vibration, creating a more accurate weapon. The disavantage is that the narrow tube frequently becomes clogged with the residue of the powder. Also, the hot gas causes the mechanism to overheat and jam.
Like any large institution, the US military is reluctant to make changes. It has continued to promote and produce the weapon for 45 years despite the known faults. And troops continue to die for this intransigence.