A modular pistol has a frame having an elongated grip portion, a linear grip interface on the elongated grip portion, a first element configured to slidably engage a first portion of the linear grip interface, and a second element configured to slidably engage a second portion of the linear grip interface. The linear grip interface may be a track having a constant cross-sectional profile. The linear grip interface may be on a rear portion of the elongated grip portion. The first element may be configured to slide over the second portion of the linear grip interface and reside on the first portion of the linear grip interface. The first and second elements may abut each other. The first element may be a beavertail. The second element may be a backstrap. The first and second elements may each have a flush contoured surface continuous with each other.