Hi,
The VoPo magazines are basically the normal Haenel-Schmeisser extruded type magazines, but with a base made out of 'grauguss', a sort of soft, cheap metal also used for toy cars. (can't recall the proper English phrase for the stuff).
As the Haenel plant ended up on the wrong side of the border in what later would be DDR-land, the site was set up to produce for the Eastern-German government. Besides the production of the magazines, they produced barrels, reworked P08's and produced a Walther PP/PPK version, known als the 'Pistole 1001'.
The '1001' code found on VoPo mags is the 4-digit company code for Haenel, btw.