From top to bottom, left to right:
XBRT-60: Derived from the Stoner AR-16, this weapon was never actually adopted, but served as the basis for the AR-18, which would in turn become the ART-65
ART-65: The original infantry rifle
ART-65C: ART-65 Compact, a light carbine designed for vehicle crews, officers, and other troops who would not normal be issued a full-sized rifle.
ART-65CS: Compact, Suppressed. This weapon, chambered in .338 (8.53x42mm) Nightowl instead of 7x42mm SPAC, was almost totally silent, and devastating even to foes with body armor. It was favored by special forces of New Corda and other NACO countries.
ART-65M: Modernized. Original furniture was replaced with tougher, more modern black polymer, NACO M1913 PCAPs were added to the top, sides and bottom of the rifle. Currently in service with the Cordian Home Defense Corps Reserves, and Civil Militia.