Part of a small array of hand tools displayed in "America On The Move" - such tools were used in the inspection and repair of steam locomotives. Light repairs on steam locomotives were usually done in roundhouses at the many small locomotive terminals throughout a railroad's system; heavy repairs were done in a large, centralized repair shop serving the whole system (often referred to as the "Back Shop"). Most of these tools date from the early- to the mid-20th century, roughly 1900-1955.
Rivet guns came in various sizes. Such guns as the one here were pneumatically powered, i.e., powered by high air pressure, fed by a special hose from the repair shop's compressed-air system to a quick-disconnect on the gun itself.
When riveting, a steel "buck" (or another rivet gun) was held strongly by a second person against the small end of each hot rivet. Thus, as the riveter hammered a hot rivet home with his gun, the end of the rivet on the opposite side from the rivet gun would blossom out into a shaped head and create a tight joint. "Riveter" and "bucker" worked together, while the "heater" heated fresh rivets to a high temperature in a small furnace and tossed them up, one at a time, to the riveter. The riveter (with his gloved hand) or a junior assistant caught the rivet and inserted the rivet in the hole. Riveter and bucker then quickly drove the rivet home, shaping it into a tight fit before it cooled.
Rivet guns were used with variously shaped "swages" (a "swage" is the small tool inserted into the business end of the gun) to hammer home rivets with different shaped heads, to cut pieces from thin steel sheets (with a cutting swage, like a fast moving chisel), or to shape the ends of tubes and flues on the inside of boilers ("curling" the ends of tubes with a shaping swage). A small gun of this type was also used in welding work, often to break old welds in thin steel.
See Swages for Rivet Gun in this database.