Pieces of steel in cylinder??

More low metal temp metals....

Low Temperature Metals for Casting in 3D Printed Plastic Molds

They are alloys of bismuth, lead, tin, indium, cadmium, thallium, gallium and antimony in different proportions. Some commonly available fusible alloys are Rose’s Metal, Wood’s Metal and Field’s Metal. All of these have melt points less than 100C, and Field’s Metal melts at only 62C. All of these would be perfectly suitable for casting in 3D printed plastic.