The invention relates to a piston (5) for a printhead (1) of a 3D printer, particularly a metal printer, comprising a piston rod (17) and a ram (18), the ram (18) having a discharge side (19) that has a convex or tapering surface (39). The invention also relates to a printhead (1) for a 3D printer, particularly a metal printer, comprising a housing (3), a device (28) for supplying a metal (14), a reservoir (7, 27) for a liquid phase (8) of the metal (14), a nozzle device (2) comprising a guide sleeve (11) and a nozzle plate (9), and a piston (5) according to one of the preceding claims, the ram (18), the guide sleeve (11) and the nozzle plate (9) forming a displacement chamber (21), and the ram (18) and the guide sleeve (11) forming at least one area (40) for conducting the liquid phase (8) between the reservoir (27) and the displacement chamber (21).