Israeli IMI Galil Short Automatic Riffle in the carbine/compact configuration. The AR version is the standard bigger version with the bipod. I believe there is an even smaller version of the rifle than this one for PDW use. The Galil was the Israeli assault rifle that replaced the FAL in Israeli army service, it was later itself replaced by the Tavor rifle. Galil's were manufactured in 7.62 and 5.56 NATO but they are more commonly found in 5.56. If you want to learn a detailed history on the rifle Forgotten Weapons has an excellent video on the Galil.