The Rheinmetall Steyr RS556 is a Austro-German modular assault rifle.
The RS556 was jointly created by Rheinmetall and Steyr as a modular weapon system to potentially replace the Heckler & Koch G36 currently in service.
The RS556 is looks similar to an AR-15, but is a derivative of the Steyr AUG. It is based on the Steyr STM556, an assault rifle Steyr announced in 2012. The rifle is available in three configurations; assault rifle, carbine and light machine gun configurations, has four hammer-forged barrels of different lengths which can be replaced without tools and a special service coating which allows the weapon to work without lubrications. It has multiple Picatinny rails, such as MIL-STD-1913, STANAG 2324 and STANAG 4694 rails, which allows it to mount various accessories and optics. The RS556 is claimed to have a special breech system with an "emergency operation feature" which allows it to operate reliably in extreme conditions such as extremely hot weather. It is compatible with Rheinmetall's "Future Soldier - Expanded System" and can be connected to other similar systems.