According to this:
http://www.armytimes.com/news/2011/0...-2011-010111w/

The MK48 will serve as the fire team automatic weapon. It is 32 percent lighter than the 27-pound M240B, but lacks its effective range.
The US Army appears to be adopting the Mk 48 as their fireteam automatic weapon in Afghanistan. The quote is brief, however, and I haven't been find much more info on it.