I have seen pictures of M60 firing mechanisms arranged incorrectly. I don't remember the sequence of firing pin, sleeve, spring that allowed an incorrect sequence, but it happened. It is my opinion that any service weapon that makes it into the field, where parts may be assembled out of sequence, or in the wrong orientation, to be a bad design. Good designs, such as the M98 Mauser, the bolt parts only assemble one way, and the correct way.
I was surprised to find how lacking many are in mechanical aptitude. A retired Major I know, Vietnam Combat veteran, twice came to me because he could not reassemble his Mosin Nagant rifle bolt. Major is not stupid, he just can't see the interrelation between the parts. He can be trained, by rote, to disassemble and assemble things. No weapon should make it out to the field that requires the skills of a mechanic, or a mechanical engineer to operate, maintain, etc.
I was surprised to see how complex the K31 bolt is
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I think the Swiss K31 design shows how well the Swiss are educated even at the High School level, or the weapon would have been too difficult for the average Swiss ground pounder.
As a comment on the American Educational system, a couple of decades ago I read the book
What is Total Quality Control? The Japanese Way by Kaoru Ishikawa. This book was an English translation of a Japanese book for Japanese factory workers. Workers who were standing or sitting on factory floors assembling things. What surprised me was the level of statistical knowledge assumed to be known by Japanese factory workers. There was a discussion of median, mode, average, and the normal distribution, and probability. Eventually the book got into statistical identification and tracking of deficiencies. The people being taught did not go to University, and yet, did not need to be "spoon fed" to understand what these things were, as these mathematical concepts were only there to show how they related to Quality Control.
A population educated to the level of the Japanese and Swiss can be handed more complicated weapons than American populations whose primary educational system graduates individuals who are illiterate, and can't add or subject without a calculator.
But at least American High School graduates can identify who is a victim, and who is an oppressor. And can explain what "equity" means.