Lots of excellent info here but I can only go on personal experience. During my 30 yr. LEO career I had the unfortunate experience to be involved in more than one duty related shooting, every time using the .38 +P FBI round. It just works, but shot placement is king and do not count on a one shot stop, that is pretty much a myth.

In retirement I continue to carry a J frame .38 w/confidence, you could do a lot worse.

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Old Cop
LEO (Ret.)