Perhaps Saddam Husain's super gun - there was only ever one made and it is a bit bent now.
The biggest Nerf gun ever would have to be the Ultimator. Despite beliefs that the Stampede is the biggest, the Mattel Ultimator from 1995 is the largest to date. Second largest would probably be the Pulsator from 1998.
The Paris gun made by the Germans in WWI.
The biggest gun ever used is the Schwerer Gustav which was a German Railway gun used in WW2 it had an 800mm shell with each shell weighing up to 7.1 tonnes
The Railway gun the Germans used to shell Paris in WWII
Are you talking bore size or physical size?
i believe the 1st ever gun made was made from cast iron and was dated from the 13-15 century made by the Chinese
The first paintball gun was a pump gun. The year is unidentified.
The first was the gatling gun invented in 1862