From The Manufacturer/Wikipedia/People Smarter Than Us:
The Thunder Pro HC provides decisive stopping power and was built to perform under adverse conditions. Originally developed as a military/law-enforcement sidearm, the Thunder Pro HC offers the same rugged durability, shooting accuracy and mechanical reliability of our signature 380 line.The Thunder PRO is an excellent choice for anyone preferring a high capacity handgun. Choose from a 17 or 13 round magazine (9MM vs .40 S&W respectively), and you have one of the highest capacity handguns available.