VERA Super Spud Gun

VERA is a low cost, low acceleration, compressed charge combustion gun featuring a 40 foot (12.2 m) barrel and a 19 inch (483 mm) bore. VERA was designed to minimize payload acceleration forces, accommodate large and/or oddly shaped projectiles, and allow for in-barrel instrumentation and control of energetic or inert payloads.

And yes, VERA, can best be described as a “potato gun on steroids.” Quite probably the world’s largest and most powerful, but no research to back up such a claim has been made.