Officers seized a white and black replica 3D-printed bolt action pistol from the 17-year-old yesterday morning after a tip-off from the public.
Later in the day, police searched the boy's home at Garran and uncovered three more 3D-printed weapons.
They included a silver 3D-printed replica .44 magnum revolver, a black and green 3D-printed replica rocket-propelled grenade and a black 3D-printed replica .50 calibre revolver pistol, as well as 3D-printed ammunition.
"Police would like to remind the Canberra community that the manufacturing of 3D-printed weapons is illegal," ACT Police said.
"3D-printed firearms are considered illegal weapons."
A police spokesperson said no charges have been laid at this stage.