[1] The Oerlikon SSG36 anti-tank rifle demonstrated, that it was possible to build a successful straight blowback rifle up to 20 mm caliber shooting at 750 m/s (2,500 ft/s) velocity.
The SSG36 used a Becker principle of bolt head following the rebated rim cartridge base deep into the chamber.
The blowback action Oerlikon SSG36 has a deep chamber in which the cartridge totally sinks along with the bolt head.
The massive recoil of the 20 mm cartridge was quite effectively tamed by the straight blowback operation and the mass of the bolt creating much less vigorous kick than regular delayed blowback actions.
Some numbers were delivered to Bolivia and saw service during the Chaco War.