The new round replaces the current M855 5.56mm cartridge that has been used by U.S. troops since the early 1980s. The M855A1 resulted in a number of significant enhancements not found in the current round, which include improved hard target capability, more dependable, consistent performance at all distances, improved accuracy, reduced muzzle flash and a higher velocity.
Army begins shipping improved 5.56mm cartridge
http://www.army.mil/-images/2010/06/23/78219/size0-army.mil-78219-2010-06-24-060658.jpg
Army begins shipping improved 5.56mm cartridge
http://www.army.mil/-images/2010/06/23/78219/size0-army.mil-78219-2010-06-24-060658.jpg