National Metallic Chamber Casting Alloy is the best known material from which to make a casting of the chamber and throat of a firearm - to determine caliber or check the dimensions. It melts at a temperature just above 158*F so all you need is a propane torch and a bullet casting ladle. It can also be used to make a cast of a dovetail slot or any other hard to measure area. Also, it is great for removing the front half of a case from the chamber, in the event of case head separation; and lots of folks cast a small portion of the barrel to determine bore diameter. For best results, measure the casting one hour after casting. Contains 42.5% Bismuth, 8.5% cadmium, 37.7% lead, 11.3% Tin. Notes:Plug the bore immediately ahead of the throat of the chamber using a small cleaning patch.Pour the alloy directly into the chamber until full and allow it to cool, it will turn a shiny silver color. As soon as it has cooled enough that it is no longer a liquid (and doesn't present a burn hazard),...