A replica of the 7.62 x 25 mm Tokarev pistol cartridge (used in the pistol of the same name), which is nearly identical to the older 7.63/.30 Mauser cartridge used in the famous "broomhandle" C96 Mauser pistol (a.k.a. Han Solo's DL-44 blaster) of 1896.
Dimensions were taken from the Lyman's Reloading Manual, 49th edition, and the model built in FreeCAD. The completed ABS "snap cap" (inert replica used to test-fire a gun without leaving the chamber empty) was tested in a Romanian TTC pistol.
As this is a digital copy of a design that's 124 years old, it's entirely in the public domain.