2 sides of this discussion must be considered in making a choice.
1. If is for convenient pocket carry to be produced, placed in a bad guys face and then shoot...what ever fits your pocket and you can hit something more than once at 7 to 10 feet will work.
5 shots into 5 inches @ 5 feet, in under 5 seconds as Crazy John @ PROLOAD Distributors says !
2. If you are talking being able to fire from a pant or jacket pocket, forget about an auto. One shot and you will be jammed, unable to fire again.
Now enter the derringer or revolver....now you are talking repeat shots without having to deal with unrestricted slide travel, ejection and reload issues. a S&W J frame or Taurus 85 type 5 shot revolver is ideal, ahmmerless like a bodyguard or centennial is even better because a hammer spur MAY catch on clothing and ruin the rest of your life.
With all the auto's out there, law enforcement still relies upon and issues J frame revolvers to under-cover type officers because they DO work !
They do come in 357 Magnum but WILL ignite the jacket pocket when fired !
AMMO: go for something specifically designed for short barrels....the load from CCI/Seer Gold Dot is a worker.
Hope that helps !