Is this the delinked stuff in the brown Talon boxes? If so, it groups like one would expect mixed lot MG ammo to group. If in sealed cartons of the same lot, it could go for a bit more.
- - - Updated - - -
Probably LC53 headstamp, sold off by the CMP a few years back. .60/round or so, IIRC. It's old but that is good shooting ammo, and NC.