A reader of the blog found this magazine in a box of junk being thrown out. Apparently it was found in the locker of an old timer who retired. The company he works for manufactures ordnance and fuzing for the military.

The magazine is cast or extruded aluminium, definitely not stamped. The follower has an articulation that looks like it is designed to push the nose of a cartridge up.

Can anyone identify what gun this magazine belongs to?

[ Many thanks to aka_mythos for the photos. ]