Sources seem to vary on whether this cartridge is called 5mm Clement or 5.4mm Clement, but it's a scarce chambering used briefly in the early 20th century, with a steep bottlenecked cartridge that reportedly developed over 1,000 fps from a short barrel pocket pistol.  Used primarily in Clement and Anitua & Charola pistols.  Model i.d. is complex with many variaitons. Good info on early Clements can be found at   

CONDITION: Very good with about 95% blue and a few usage dings.

ITEM #B419   S/N 7699   CAL 5mm Clement

B419 Clement 5mm pistol