If it was 7.62x51 it was not from a M249. The M249 or SAW fires the same 5.56x45 round that the M4, and M16 do. Perhaps it came from the M240, or M60 machine gun. It should be fine to reload, just check for wear since belt feds are hard on brass.Recently a friend gave me about 500 empty 308 cases fired from a M249 machine gun. The headstamp is LC. Are these OK to reload and use in a semi-auto rifle?