Even with the pin in the bolt carrier modification, the pin can get worn or break, and it is possible to assemble the bolt wrong. If the bolt was originally assembled wrong, and fired that way, the right hand lugs would be on the left side of the action, and thus be sheared. If the bolt was then assembled correctly, the sheared lugs would then be on the right side of the bolt.

It takes a lot of effort, but it is possible to wrongly assemble a pinned bolt. It can be done!
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