Abstract: The injection chamber (CI) includes a tubular body formed by a supply portion, having a radial supply window to receive a charge of molten metal (MF) and in which is incorporated an injection portion provided with an outlet end opened to the interior of a molding cavity. A piston is provided to be displaced in the interior of the tubular body to inject the molten metal (MF) in the molding cavity. The supply portion has its inner region, which receives the pouring impact of the charge of molten metal (MF), lined by an insert formed in a high melting point material and presenting an inner contour in the form of a circle arc coinciding with that of the supply and injection portions.