The Breda PG (“presa gas” – “gas operated”) was an open-bolt, select fire rifle that saw only very limited commercial success. Approximately 400 were made in 7x57mm for the Costa Rican military (it used the same bayonet as the Costa Rican Mauser rifles). Its most interesting feature was the use of a 4-round burst mechanism instead of unlimited fully automatic fire. The PG was also one of several guns of the period designed with the feed lips integral to the receiver, rather than being shaped into each magazine.
The Breda PG uses a rising bolt design with a locking lug on the top of the receiver. As the bolt and carrier move forward under pressure from the recoil spring, the bolt is forced upwards, engaging it against the locking lug. A gas piston running inside the handguard pushes the bolt carrier back upon firing, which in turn cams the bolt downward and unlocks it.
Breda PG (click to download high-resolution copies)
Photos of another Breda PG (click to download high-resolution copies)
Breda PG magazine (click to download high-resolution copies)