>>64276909
I believe there was a similar prototype attempted IRL, and the notion may have been to get high capacity but without the wide bulk of the regular drum. Possibly they also hoped to develop better and more consistent manufacturing, so that the helical mags would more freely interchange between guns, something that wasn't the case with the PPSh-41 and its drums, but was generally the case with the 35rd sticks.

There actually existed a prototype sideways drum for the PPSh-41, the notion being to retain similar capacity but to make the weapon much flatter, but obviously they never went with it.
Possibly it never really worked well, or maybe they felt it wasn't enough better that it was worth pursuing, just keep cranking out what they have tooling for and then match drums and guns as much as they can, etc.