An ammunition magazine including a housing having a first end and an opposing second end for carrying stacked cartridges, a follower plate reciprocally movable within the housing, a spring retainer reciprocally movable within the housing and having an extension tab extending therefrom toward the second end, and a biasing member carried by the housing between the follower plate and the spring retainer. The biasing member biases the follower plate toward the first end and biases the spring retainer toward the second end. A bottom plate closes the second end of the housing and retains the spring retainer within the housing. The bottom plate includes an opening extending therethrough permitting passage of the extension tab therethrough in reciprocal directions.