Hints For Using Cerrosafe

By Mike Watkins

We’ve recently fielded a lot of questions on the Tech lines and by email about casting chambers using Cerrosafe casting metal. The following is some information about Cerrosafe that Cerro Metal Products has provided us with.

“The basic ingredient of Cerrosafe is bismuth. Bismuth is a heavy, coarse, crystalline metal that expands when it solidifies, up to 3.3% of its volume. When bismuth is alloyed with other metals such as lead, tin, cadmium and indium, this expansion is modified according to the relative percentages of bismuth and other components present. As a general rule, bismuth alloys of approximately 50% bismuth exhibit little change of volume during solidification. Alloys containing more than this tend to expand during and those containing less tend to shrink during solidification.”

What this all means for the gunsmith is that you can make an extremely accurate chamber castings using only Cerrosafe and a few simple hand tools. To make a chamber casting, first clean and degrease the chamber. Use a tight-fitting cotton patch that’s wrapped around a bore mop or brush to plug the bore just ahead of the throat, which means you have to insert the plug from the muzzle. I usually leave the cleaning rod attached to the plug until it’s time to remove the plug. Melt the entire bar of Cerrosafe in a heatproof container from which you can easily pour the hot Cerrosafe. You can use a propane torch on the container or heat over a hot plate or the burner of a stove. Cerrosafe melts easily at 158°-195° F. While the casting metal is still liquid, stir very well, skim off the dross and pour carefully into the chamber. Just be careful, it's really very easy to do. The real trick with Cerrosafe is not to overheat it. If you heat the solid slowly and keep it within the required temperature range, you shouldn’t get any dross. In actual use, you don't even need a thermometer. When it melts and goes "glossy silvery", its ready. Take it immediately off the heat to prevent dross forming.

Note the time the casting was poured. The casting will take only a very short time to solidify, usually within a minute. Wait 30 minutes and then remove the plug from the bore. Turn the muzzle upward and the casting will fall from the chamber. Catch on a towel to keep from "dinging" it anywhere. At 30 minutes after the initial solidification, Cerrosafe shrinks slightly so removal is very easy. Allow the new casting to cool thoroughly then measure the casting exactly one hour from the time it was cast. By this time, the Cerrosafe has returned to its exact cast size. Thus, the casting will give you an exact measurement of the chamber.

Cerrosafe casting metal can be used over and over in the shop. Simply re-melt the entire amount back together and pour it into a small mold of an appropriate size. Remember, always melt the entire Cerrosafe ingot to make a chamber casting. For the best results, never cut off or use just a part of the ingot.