Rimfire ammunition is a type of firearm cartridge that uses primer located within the rim of the case to ignite the propellant. Rimfire cartridges are generally less powerful than centerfire cartridges, which use a centrally locate primer to ignite the propellant.
There are two types of rimfire ammunition- in-line and Flip-cap. In-line rimfire cartridges have the primer pan located in line with the case, while flip-cap has the primer pan located 90 degrees from the case. In terms of their designs, both in-line and flip-cap messages are considered “rimless” since there is no exposed or raised rim.
The first recorded use of brass-cased, combustible rimfire ammo was in 1845. The first lead-free rimfire ammo wasn’t available until 2007. Rimfire ammo is most commonly used in pistols and rifles, but it can also be used in shotguns.