Comments by "ZGryphon" (@ZGryphon) on "Hopkins & Allen XL-6 Revolver with a Surprising Swing-Out Cylinder" video.

It probably wouldn't happen nowadays, since the current patent code requires that an innovation be non-obvious to be patentable, but those were different times. (You could patent a new non-obvious process for making the holes, but the holes themselves would probably not pass muster with a modern patent judge.)
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@korbetthein3072 People did know what metallic cartridges were at the time, they were just still too hard to produce in quantity to be cheap enough for widespread adoption. It should've been obvious to anyone who was paying attention that, once practical mass-production techniques were developed and the costs came down, the system had so many practical advantages that it would take over.
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