derringer
AMT Backup.
.17 to 20x110 Hispano
what do you mean smallest ? smallest diameter bullet ? smallest case ? 5mm , or 22 high power, 17 rem , be specific .
In a pure sense, it is a measure of the diameter of a bullet, usually given in decimal fractions of an inch (a .357 bullet is about.357 inches thick) In a broader sense, it is the cartridge that a given weapon will fire- such as caliber .38 Special, or caliber 30-06.
17 Remington.
A handgun. Some European pistols were .32 caliber, and would have been the smallest used, but many .22 caliber rifles were used in training.
In the usual sense of caliber, it means the diameter of the bullet. The smallest commercial caliber is the .17 rimfire, but there have been MUCH smaller caliber firearms, down to the 1-2 mm range. That is about .05 to .10 caliber.
Close. a .38 caliber is usually closer to .357 caliber.
.22 Long Rifle - the Sig Mosquito
POSSIBLY a rimfire revolver known as the Swiss Mini Gun. It is caliber 2.34mm, or about .092 caliber. It is not available in the US to due laws regarding import of firearms.
.40 S&W cartridge, bullet diameter = .401" .380 ACP cartridge, bullet diameter = .355-.356" .32 ACP cartridge, bullet diameter = .311 - .312"
I believe the smallest bullet in terms of diameter is the .17 HMR. It is a .22 casing that is necked down to accept a .17 caliber bullet.