Kiertoperäinen

Kiertoperäinen is a Finnish term that describes a type of firearm action. Literally translating to "rotary breech" or "rotating breech," it refers to a mechanism where a bolt head rotates to lock into the receiver. This rotation is typically achieved by turning a handle or lever.

The core principle of a kiertoperäinen action involves a bolt with lugs that engage with recesses in the barrel or receiver. When the bolt is operated, it slides rearward, and then its head rotates to unlock from these recesses. This allows the bolt to be fully withdrawn, ejecting the spent cartridge. Upon closing, the bolt slides forward, and the lugs rotate to re-engage, securing the action for firing.

This type of action is common in many bolt-action rifles and some semi-automatic firearms. It provides a strong and reliable lock-up, essential for safely containing the pressures generated during firing. The rotation of the bolt lugs into the receiver is a key characteristic that distinguishes it from other actions, such as straight-pull bolts or falling block mechanisms. Examples can be found in sporting rifles used for hunting and target shooting, as well as military firearms. The design prioritizes strength, accuracy, and user safety through its robust locking system.