Mossberg 500AR 12 GA Pump Shotgun review. After over 50 years and over 10 million sold, the Mossberg 500 is the only pump action shotgun to be declared MilSpec. In a word, that translates to “reliability”. The Mossberg 500 is one of the most versatile and reliable shotgun platforms available and the list of options offered for the 500 should fulfill just about any use you can imagine. As such, the Mossberg 500 has been presented in a wide range of models to fit every application, and every user from household, to law agencies, to military applications worldwide. Includes detailed demonstration of disassembly and reassembly.