MR556 did not allow for this, as the take-down pins were located in a "non-standard" location. The MR223 maintains the "non-standard" location of the pins, disallowing attachment of the upper receiver to the lower receivers of any other M16/M4/AR-15 family of rifles. As of 2012, the MR556A1 upper receiver group fits standard AR-15 lower receivers without modification, and functions reliably with standard STANAG magazines. HK-USA sells a variant under the MR556A1 Competition Model nomenclature; it comes with a 14.5" free-float Modular Rail System (MRS), 16.5" barrel, OSS compensator and Magpul CTR buttstock. The firearm's precision is specified as 1 MOA by Heckler & Koch. In Europe, the MR223A3 variant is sold with the same cosmetic and ergonomical improvements of the HK416A5. The French importer of Heckler & Koch in France, RUAG Defence, have announced that they are going to sell two civilian versions of the HK416F, named the MR223 F-S (14.5" Standard version) and MR223 F-C (11" Short version). Users See also Heckler & Koch HK417 Haenel MK 556 List of assault rifles List of carbines M16 rifle Beretta ARX160 IWI Tavor QBZ-95 QBZ-191 SA80 Steyr AUG FN SCAR References External links 2008 Heckler & Koch Military and LE brochure 5.56×45mm NATO assault rifles Short stroke piston firearms Modular firearms 416 Post–Cold War weapons of Germany Police weapons ArmaLite AR-10 derivatives AR-15 style rifles Weapons and ammunition introduced in 2004