The gas automation is configured to use “sports” cartridges with low charge loads. Detachable box magazine enhances the operability, the presence of the guide shaft on the receiver, further accelerates and simplifies magazine changes. The gun is provided with an automatic slide catch and quick magazine release button located under the thumb of the shooting hand. Interchangeable choke tubes enable efficient shot firing with shot and slugs at different distances. The Saiga-12 340 has an efficient muzzle brake that is worn on top of choke tubes. The fuse is designed as a transverse button located above the trigger guard. On the left side of the bolt is another cocking handle, for which a corresponding slot was cut in the cover of the receiver. The Saiga 12 340 is equipped with a telescopic adjustable plastic butt-stock with a rubber cushioning pad and an elongated forearm. The hinged lid of the receiver has an integrated Picatinny rail for easy installation of various precision optics.