never a dumb question.
only by the size of the bore. That said, the 7.65mm (or 30 luger) will go into the front of the barrrel, while a 9mm will not fit into a 30 luger.
You can "usually" tell by a picture and in real life fairly easy to tell.
Also, both cartridges will fit in the same luger magazines, and are interchangeable.
Ed
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Edward Tinker
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Co-Author of Police Lugers - Co-Author of Simson Lugers
Author of Veteran Bring Backs Vol I, Vol II, Vol III and Vol IV
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