I have this 3-cell, pebble grain black leather pouch and can't recall how I acquired it or what it for originally. It looks like it would fit Suomi Coffins.
It looks like a post war, Warsaw Pact holster for angular magazines; possibly handgun magazines. I can't gauge the size very well, but it looks relatively small.
Looks like it would accept 3 magazines of roughly 8 to 8 1/2" length by 1 1/2" deep by 1 3/8" wide. I think the dimensions are too large for a handgun.