http://en.wikipedia.org/wiki/PPSh-41
Though 35-round curved box magazines were available from 1942, the average infantryman would keep a higher-capacity, 71 round, drum magazine as the initial load.[2] The PPSh-41 drum magazine was a copy of the Finnish M31 Suomi magazine which held 71 rounds, but in practice, misfeeding of the spring was likely to occur with more than 65 or so cartridges.[5] The standard load was probably one drum and a number of box magazines, when box magazines were available.
PPSh-41的彈鼓是彷製自芬蘭 索米衝鋒槍的71發可卸式彈鼓 ，但在實際使用中如果裝載的子彈數多於65發，可能會出現無法正常供彈的情況，所以一般只裝填65 發左右的子彈。 [5]一般步兵的标准携弹量是一个彈鼓加几个弹匣。 [5]一般步兵的標準攜彈量是一個彈鼓加幾個彈匣。
Some of the PPSh's drawbacks included the difficulty of reloading, the tendency of the drums to jam (solved by the box magazines)
PPSh的缺點包括難以重新裝填，裝填71發時彈鼓容易卡殼（35發彈匣解決了這一問題）
http://world.guns.ru/smg/smg02-e.htm
Early PPSch-41's were issued with drum magazines with capacity of 71 round, similar to ones used in PPD-40.
Such high capacity increased the firepower but the magazines were too slow to refill and not too reliable, so in 1942 a curved box magazine was developed. This magazine held 35 rounds and was much more comfortable to carry in pouches. Early magazines were made from 0,5 mm sheet steel and were somewhat unreliable. Later magazines were made from 1 mm steel and were completely satisfactory. Usually, infantrymen carried one drum in the gun and some box magazines in the pouches or pockets.
