Various products are available on the market for creating a cast of a gun chamber. To ensure that we offer the most effective and practical solution, we consulted the original manufacturer. They recommended Cerrosafe due to its distinctive properties. Unlike Woodsmetal, which expands upon cooling and cannot be removed from a gun chamber, Cerrosafe contracts during the first 30 min of cooling and then, after one hour, matches the exact chamber size. After 200 hr, it expands by approximately 0.0025 inches. This characteristic is well-known among toolmakers, who will account for it when fabricating dies, reamers or gauges from your cast, provided you inform them that the cast is made of Cerrosafe. Cerrosafe melts at temperatures between 158 deg F and 190 deg F. It should be melted in a clean, iron ladle and the heat source should be removed as soon as the alloy is fully melted, at which point it is ready to pour. The solidified casting should be extracted from the chamber before or as it cools to room temperature. If left in the mold for over an hour, it will adhere to the chamber walls, making removal difficult. Thoroughly clean the rifle chamber, then plug the bore immediately ahead of the throat with a small rag, ensuring it is not so tight that it cannot be driven out. If possible, pour the molten Cerrosafe through a small tube into the bottom of the cast, gradually withdrawing the tube as the chamber fills. If the barrel is cold, warm it to room temperature or above before making the cast. Once cooled, remove the cast from the chamber using a rod or dowel inserted from the muzzle end of the gun.