The Cobray Pocket Pal is an interesting little self defense gun. It is a break open revolver with interchangeable cylinders. It is chambered in .380 and .22LR. The top barrel is chambered in .380 acp while the bottom barrel is chambered for .22LR. The .22LR cylinder holds five rounds while the .380 cylinder only holds three rounds.
The cylinders are indexed so when you shot the last round, the cylinder locks the trigger and you cannot fire the gun so you have to remove the cylinder and reload it.
Here is a video showing the inner workings of this simple firearm.