I'll venture the guess that, when the revolver was fired, the top latch was not closed securely. The energy of the firing caused the barrel to pivot away and down from the frame but the center pin (thumb latch) momentarily prevented the cylinder from moving forward with the barrel as the round was expelled causing the bent quill. S&W did include, in their lid instructions, the admonishment about making sure the barrel latch was secure. This is an example in my opinion.

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Mike Maher #283