Kiertoperäisillä

Kiertoperäisillä refers to a Finnish term describing a type of firearm action. In essence, it denotes firearms that utilize a rotating bolt or bolt carrier to lock the breech during firing. This mechanism is commonly found in semi-automatic and automatic rifles, where the rotation of a bolt head within a receiver locks the chamber, allowing for controlled firing and efficient extraction of spent cartridges.

The operation typically involves the bolt carrier moving rearward under the force of expanding gases from the fired cartridge. As it moves, a camming surface interacts with a lug on the bolt, causing the bolt to rotate and disengage from the receiver's locking lugs. This allows the bolt carrier to continue its rearward travel, extracting the spent casing. Upon returning forward, the bolt is re-indexed, and a fresh cartridge is chambered, with the bolt rotating to re-engage the locking lugs, preparing the firearm for the next shot.

This design is known for its reliability and is a cornerstone of many modern military and sporting firearms. Examples of firearms employing a kiertoperäinen action include many Kalashnikov variants, AR-15 style rifles, and other designs that prioritize robust locking and efficient cycling. The specific implementation of the rotating bolt can vary between different firearm models, affecting aspects like the number of locking lugs and the overall design of the bolt carrier group.