A modular magazine well insert system accepts and latches different types of magazines including front and side catch styles. The system includes a plurality of magazine well inserts each having a common mounting interface which interfaces with a mounting feature formed in a receptacle of the firearm stock. The inserts may have a common basic configuration with some different features adapted for use with different magazine catch features, such as latching levers for front catch magazines or lateral apertures to access side catch magazines. A universal latch stud slideably mounted in the stock comprises features which cooperate with each of the magazine well inserts to retain and release both catch styles of magazines in the insert.