I didn't see where German wanted the pistol for self defense.
The way I read his OP he was just curious about the use of a little .31 pistol "back in the days".
IMO, the little .31's were popular because of their light weight and the ease of concealment.
Adding up the Patersons, 1848's, 1849's and Roots, Colt made over 370,700 .31 caliber cap and ball guns. Then we can add the Manhattan Pocket pistol (4,800), Remington-Beals 1st model (4,700?), Remington-Rider (2,000), Remington New Model Pocket Revolver (25,000) and numberless copy-cat clones and small Derringer and boot pistol single shots and one can see that the little .31 caliber "mouse gun" was very popular indeed.
There are of course many larger caliber pistols that were used during the mid 1800's that were more effective but these were also larger and more difficult to conceal.
"My Lady" of that era would rather be caught dead than to walk down the street with a military sized handgun and most "gentlemen" then also wanted an easily concealable defensive arm.
I think we modern people put too much faith into muzzle energy. The little .31 with a full chamber load was/is quite capable of penetrating from the front to the back of a human if the shot is in a soft area like the stomach.
Such a wound in the 1800's would often be fatal. As others have mentioned, it might not be immediate but within a week most people shot in the mid-drift could look forward to a slow, painful death. Not something to be taken lightly.
