The Colt IAR is Colt’s entry in the Marine IAR competition for a lightweight automatic rifle to replace the SAW in certain situations. It is an interesting weapon.
Under the barrel you can see a hefty heatsink. This is used to prevent cook-offs (when the primer of a chambered round is ignited by a hot chamber). It weights 9.5 lbs and has a 16″ barrel.
It looks like the barrel may be be changed by simply removing the bolt you can see just in front of the magazine well.
Surprisingly the rifle/machine gun does not use a gas piston and uses the AR-15/M16 direct gas impingement system.
The above photo does show a Magpul PMAG but the Marines have specified that the IAR must be compatible with 30 USGI magazines, so it is unlikely the military will be adopting PMAGs, even in a limited role with the IAR.
Other IAR entries can operate with either an open bolt, in automatic fire, or closed bolt in semi automatic mode. This allows the accuracy benefits of a closed bolt with the heat reduction and reduced chance of a cook off of a closed bolt. I am not sure if this weapon has this feature.
Colt already have a lightweight automatic rifle, the Colt Automatic Rifle (CAR), which itself may meet the Marines requirements. I do not know if the Colt IAR has anything in common with the CAR, other than the shared AR-15 heritage.
UPDATE: Defense Review has more info.Related