Take it from someone who has been there, stopping power is a myth. Best I can offer is to carry the largest caliber you can handle and practice, practice, practice. Personally I carry a J frame loaded w/+P .38 Speer Gold Dot. When deep concealment is needed I'll carry the LCP loaded w/HPR hollow point 90 grain. UPDATE: I just read a lengthly article written by a cop who had worked a lot of homicides where the .380 was used. His take is the FMJ is a better option b/c it reaches the vital organs where the HP usually stops short. Some say they use a mix in their mags but I'd check reliability carefully before doing this. Some guns choke when HP & FMJ are fed through the same magazine. My LCP is loaded w/HPR 90 grain hollow points b/c they meet the FBI tests for penetration.

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Old Cop
LEO (Ret.)