Beretta 418
The Beretta M418 is a 6.35 mm (.25 ACP) easily concealed Italian "pocket pistol". The earliest examples were made between 1919 and 1922. There are several versions, including the 1920 (V1 & V2), 1926, 1926 - 31 (V1 & V2), 1934, 318, and 418 models.
Read more about Beretta 418: Early Models, Beretta Model 418, The M418 in Fiction, Technical Data, Series Numbers