[AMX]

1) http://www.navweaps.com/Weapons/Gun_Data.htm :

Autofrettage - A process in which a favorable distribution of initial or residual stress in a tube is induced, as in the manufacturing of gun barrels. [...] During the 1920s and 1930s, the US Navy termed this process "manufacture by radial expansion."

2) common sense
3) Paul-Werner Krapke: Leopard 2, sein Werden und seine Leistung; Mittler-Verlag 1986, page 98

Also note that the video shows a Leo2A6, which uses the longer (and heavier) 120mm L55.


edit: rheinmetall-detec gives the barrel weight as only 1190kg.
'Course, that mainly means the article's figures are even further from the truth.