This is the 10 round .308 magazine for Saiga format rifles from SGM Tactical.
Manufactured from tough glass filled polymer composite with a slick gloss internal finish, the magazine feature a slightly longer spring length than other Saiga mags for improved pressure uniformity.
Civilian market Saiga magazines differ from AK/AKM pattern magazines as the rifles do not have a feed ramp in the rifle below the barrel, instead the magazine has a feed guide built into the front edge.