I recently picked up a gun that establishes just how small a true functional automatic pistol can be made. In fact, this tiny Bernardelli pistol is a fine example of the gunmaker's craft.
At one point in our history, there were a great many such guns in production, most of them European in origin. These guns were often referred to as vest pocket pistols and it was once the fashion for gentlemen to go about their business in three-piece suits that had vests. These vests had several small pockets, which were ideal for packing a small auto. Of course, the rules about people carrying guns were not so restrictive in the early 20th Century, so there was an active market.
Naturally, most of these little pistols are chambered for cartridges that fall short of dragonslayer status—either .25 ACP or .22 Short. A few made it into production as .22 Long Rifles and there were smaller numbers of .32s.
By any measurable standard, none of these are manstopping calibers, but no one seemed to care. Personally, I see guns like these as milestones. While none are ideal for personal defense in any age, they led to the modern small autos in better calibers such as .380 and 9 mm Luger. If anything, these little guns accustomed people to the idea of a flat pistol of diminutive size. Now we can work on pistols of that size class that delivers power up to the obvious demands of personal defense.