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)
chamber casting 
