The US Marines have been using the M249 5.56mm light machine gun since 1984. Many were worn from use, and at 15-17 pounds empty, these belt-fed weapons are rather heavy. They can be more hindrance than help in some of the close-quarters urban warfare situations dominating current battlefields, especially since they have a reputation of jamming more often than standard rifles.
Their initial 2005 FedBizOps.com solicitation for an “Infantry Automatic Rifle” (IAR) wanted two big things. First, the gun had to fire from either the open or closed bolt position. This would give it the single-shot and “first through the door” capabilities that the M249 lacks, while allowing for more sustained fire than an M16 can handle without risking ammunition “cook off” in a heated barrel. It also had to be considerably lighter than the M249, at just 12.5 pounds maximum and 10.5 pounds desired weight. In exchange, the Marines decided they were willing to trade the SAW’s belt-fed design for switchable 30 round magazines, which are used up much more quickly but can be changed in battle much more quickly.
The result was not a true light machine gun, but something in between an LMG and an assault rifle. That shift in the 13-man Marine squad has its advocates and detractors. DID offers more background concerning the USMC’s IAR contenders, contracts… and controversy.