Cerrosafe 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.
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), remove it from the chamber. Take care not to
overfill the chamber as the alloy will then run into the locking lug area, making removal extremely difficult.
During the first 30 minutes of cooling cerrosafe shrinks. At the end of one hour it should be "exactly" chamber size.
Melts between 158 and 190 degrees Fahrenheit
Should be melted in a clean iron ladle without direct flame on the product.
The chamber being cast should be cleaned thoroughly and a thin coat of oil or graphite applied.
Contraction - expansion factor versus time, measured in inches per square inch:
2 minutes -.0004"
6 minutes -.0007"
30 minutes -.0009"
1 hour +-.0000"
2 hours +.0016"
5 hours +.0018"
7 hours +.0019"
10 hours +.0019"
24 hours +.0022"
96 hours +.0025"
200 hours +.0025"
500 hours +.0025"
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