Carl Gustaf 20 mm recoilless rifle
The Carl Gustaf 20 mm recoilless rifle, service name 20 mm pansarvärnsgevär m/42 (20 mm pvg m/42), meaning "20 mm antitank rifle model 1942", was the first recoilless rifle produced by Carl Gustafs Stads Gevärsfaktori. The weapon had a penetration of just over 4 cm RHA with its standard solid shot armour piercing projectile and quickly became obsolete against modern armour, leading to the development of higher caliber recoilless guns, eventually resulting in the Carl Gustaf 84 mm recoilless rifle in 1948.
Source: Wikipedia — Carl Gustaf 20 mm recoilless rifle (CC BY-SA 4.0)