Detectives executed the warrant at a storage facility on McClelland Drive, Langwarrin, just after 10pm on April 2.
They allegedly uncovered a range of weapons.
As well as the explosive device, police said they seized a 3D-printed handgun, 10 rifles, two shotguns, a “substantial” amount of ammunition, and tasers.
A 39-year-old Cranbourne man is assisting police with their enquiries.
