Rat-shot

Rat-shot (or snake shot) is very small lead shot (typically #12 – 1.3 mm (0.05")) loaded in cartridges for use in rifled firearms as opposed to more traditional smoothbores such as shotguns. Rat-shot cartridges allow one to use a handgun or rifle as a low power shotgun for short-range use. Cartridges loaded with rat-shot are often called shotshells. The most common cartridges loaded with rat-shot are the .22 Long Rifle and certain pistol or revolver cartridges. Shotshell cartridges known to be available for hand guns include: .22 LR, .22 Magnum, .38 Special, 9×19mm Luger, .40 Smith & Wesson, .44 Special, .45 ACP and .45 Colt. The CCI .22 LR shotshell holds 1/15 ounce of #12 shot; the CCI .45 Colt shotshell holds 1/3 ounce of #9 shot. The smaller shot size typical of .22 shotshells is sometimes called "dust shot" and is used mainly by collectors of bird specimens.

Rat-shot is generally used for shooting at snakes, rodents, and other small animals at very close range. It is used by farmers in rifles for the control of birds flying inside of barns and sheds, as well as for killing rats, for the simple reason that rat-shot will not damage the metal roof of a barn or the metal sides of a shed, while still being effective against small pests at close distances. Rat-shot is often used in 22 caliber rifles to train new shooters in the use of a shotgun and as a first step in bird dog training for the dog to get used to loud noises.

...
Wikipedia