Steyr Mannlicher has developed an AR-15 rifle called the STM556.
The most important innovation of this rifle is the quick change barrel. The barrel can be easily remove by the removing bolts that attach the gas block onto the one piece upper receiver/handguard. The STM556 is fully ambidextrous and is fitted with a Magpul stock and pistol grip.
Steyr has finally introduced a credible modern service rifle (long ago having ceded development of the Steyr AUG to the Australians). This rifle, with its premium features, looks like a strong competitor to the SIG516 and the HK416. If the rest of the world follows the USMC lead and introduces IAR-style machine guns, the STM556 with its quick change barrel will have a distinct advantage over the before-mentioned competitors.
[Hat Tip: Strategie Technik ]
[ Many thanks to Hannes & Rolf for the tip. ]