Diecasting, such as is currently done to produce the popular metal vehicles by Ertl and Winross, involves pouring molten metal into a mold in the shape of the toy being made. The metal cools as it hits the surface of the mold, and then takes on the shape of the mold “cavity.”
Diecast toys can be either solid or hollow. Many of the early cast iron toys and soldiers were solid. They were made by merely filling molds, waiting for them to cool, then removing the solid metal toy. Later manufacturers, in an effort to cut material costs, began pouring the metal into the mold while it was spinning, causing the metal to cling to the sides of the mold while it was spinning, causing the metal to cling to the sides of the mold and cool, forming a hollow toy. This process worked well for potmetal, such as on Tootsietoy cars, and on lead soldiers such as Barclays, but it wasn’t really successful for cast iron use.
Early “hollow cast” toys tended to vary in thickness, as the technique was new and exacting methods had not yet been developed. More modern pieces tend to be rather uniform in thickness, due to exact measurement of the amount of metal poured into the mold.