The man responsible for amassing an arsenal of deadly firearms, including a loaded machine gun with five spare magazines and a semi-automatic shotgun, will spend six months in jail amid warnings his high-powered weaponry could have caused "unthinkable" damage in a crowded place.

Graham Leslie White, who is also under investigation in relation to the illegal dumping of up to 19 million litres of toxic waste in Melbourne's north, was flagged by Judge John Smallwood as a potential "red alert" for authorities given the "very scary" nature of the weapons he was stockpiling and his personality.

White faced the County Court on Tuesday to be sentenced over the haul of illegal weapons uncovered last year in a secret compartment in the bathroom of his sprawling property in Wallan, north of Melbourne.

Graham Leslie White who had enough gun power to do 'unthinkable' damage in a crowded place has been sentenced to six months' jail. Credit:Chris Hopkins

During his sentencing remarks, Judge Smallwood outlined in chilling detail the human damage that could have been caused should White’s machine gun ever be used in a "crowded" space.