The MK46 Mod 0 and M249 SPW(Special Purpose Weapon) LMG’s are basically modified, shortened, and lightened M249 SAW’s(5.56x45mm) that have been developed specifically for use by U.S. Special Operations. On both, the M249′s forearm has been replaced with a rail system, although the SPW’s and MK46′s rails are of different configuration. Also, their buttstocks differ from each other in that the SPW retains the Minimi Para’s collabsible buttstock, while the MK46′s stock is fixed. Both weapons are about 4.1 lbs lighter than the standard version due to the modifications.
For more information, as well as a pic, on the MK46 Mod 0, click on this link.
Click here to see a pic and get more info on the M249 SPW.