You'll have to give up to get: the ability to use the M16 magazine is lost, pretty well neglected or abandoned by most M249/Minimi users anyway. And the Mark 48 weighs in at 8.2 kg, a bit heavier than the 7 kg of the M249 [depending on model/configuration] or the 5.75 kg of the Navy Mark 46 Mod 0 Special Warfare lightweight 5.56mm SAW, which also deletes the magazine-feed capability as means to achieve weight reduction, but adds multiple Rail Interface mounts for scopes, laser targeting *killdots* thermal viewers and other useful accessories- some of them heavier than the gun.
The real question will be what comes of the proposed 6,8mm ammunition developments, particularly as they relate to the XM-8 rifle. Changes to the M249 to accomodate the new round should require little more than a bolt and barrel change, with a new link to replace the 5,56mm version probable, and possibly requiring some new components in the top cover/feed tray assembly. But we shall see.
