Using a two-shooter for self-defense may not be the best idea, but it certainly can be effective. If you are going to use a two-shot derringer in a defensive situation, you must plan on what you will do when you run out of ammo. The glib among us will say, “That thing will make a good club.” You know what? They are right. It will make a good club. Learn to use it as such.
The goal of self-defense is to create enough dysfunction in your attacker to ensure that you can escape safely. You may be required to incapacitate your attacker completely in order to facilitate your escape. If you are justified in using deadly force, slamming someone with your empty pistol is perfectly fine.
You must learn to fight with the tools you choose to use in self-defense. With a derringer, you have two shots. Use them wisely. Make sure they are as effective as possible. After you deliver your two rounds, you may still need to persuade your attacker to go elsewhere. That 1-pound chunk of metal in your hand can still be effective. Grip it firmly, and drive the muzzle into the suprasternal notch, right where the rib cage meets the neck. If the deafening report, blinding flash and nearly supersonic slug of hot lead did not move your attacker back, this certainly will. After that, get to a safe place because you are out of ammo and the derringer is slow to reload.
Not a Quick-Draw Unit
A derringer (or any backup gun, for that matter) is typically not something you can get access to quickly. You need to keep that in mind if you are in a situation that appears to be going from bad to worse. On the other hand, if you are the victim of a sudden assault, you will need to defend yourself with one hand while you reach for your gun.