If I remember correctly, Drum magazines also had a higher rate of FTF (failure to feed) due to dirt and grime (soldiers who didn't clean their guns and amgs properly). And the machining was setup at the time (WWII) for single stack 20 round magazines for the thompson (30 rounders didn't play a major role until around 1944). Production efficiency and magazine repair was a nother issue.
It was easier to make a single stack 20 round magazine than it was to make a 50 round drum with a spring that would be as tall as your leg.
__________________
Science is the organized unpredictability that strives not to set limits to mans' capabilities, but is the engine by which the limits of mans' understanding is defined-Yahoshua
  
|