Age, I'm sure I'm not completely correct, but what I've read is that the Krag side loading system and the single locking lug was inferior to the mauser system interior magazine and double lug. Put a Krag against a trapdoor springfield - 100% improvement- also aren't the 30-40 cartridges rimmed? This is also a problem in magazine fed guns. If not stacked right they hang up.
http://www.chuckhawks.com/30-40krag.htm
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