A method for manufacturing a solid propellant (20) includes: forming a tool (200) of layers (250) of a first material wherein cuts in the layers (250) form a first interior chamber in the tool; using the tool (200) to mold a second material in the first interior chamber; removing the molded second material (102) from the tool (200); using the molded second material (102) to mold an interior chamber (30) in a rocket propellant grain (20); and removing the molded second material (102) from the rocket propellant grain (20).