The rifle was proofed by the Zella – Mehlis poofhouse, as the word "Nitro" in script and the presence of the ledger number 113 show. The proof date is 635, June 1935, or is it 636, 1936? Rifles of this type were made for various wholesalers and retailers by the Zella –Mehlis guntrade. The actions were based on a simplified Mauser M71 design, hence the "Mauser" monicker. They were made in many sizes, from tiny ones for rimfire cartridges to giants for 12 bore "Vogelbüchsen" target rifles. But all I have seen before were single shots, as shown in the ca. 1930 Burgsmueller, Kreiensen mail order catalog:

Though neither a 5.6x35R Vierling chambering nor a full – stocked Stutzen version are mentioned by the ad, it stresses the fact these rifles being hand crafted, not mass produced. So certainly many more options were available on special order. Modell 6424 came with the tang peep sight.
IMHO the magazine was designed and added by an excellent mechanic afterwards. Most likely an one-off custom design.
Many of the pre-1940 5.6x35R Vierling rifles were chambered quite generously. They accept .22 Hornets too, at least some brands.