A firearm magazine floorplate is provided, configured to be attached to a magazine housing. The floorplate includes an arcuate back face configured to provide a stable resting platform during operation. The floorplate further includes a feature configured to mate with a corresponding feature on one end of a magazine coupler. The magazine couple is easily engaged or disengaged between a pair of magazine assemblies that each include a floorplate to form or disassemble a tandem magazine assembly.