Rotometals Chamber Alloy (158-190) 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 M&M's, 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)