Cerrosafe Chamber Casting
Cerrosafe chamber castings, if carefully executed and measured, may provide accurate radial and linear values for the shoulder, neck, free bore, leade and bore dimension however, the castings provide no breech face reference point and it may be difficult to accurately measure the critical chamber depth value ( Breech face to end of case neck cut of the chamber).
A reliable and constant model of a chamber can be made using the Impact Impression method
Heating, pouring, and measuring the resulting Cerrosafe castings within a critical time frame must be performed in a precise manner in order to obtain accurate and reliable chamber dimension values.
Cerrosafe melts at a temperature lower than the boiling point of water. After the melted alloy has been poured into the chamber and then cooled to the point of solidification, the casting shrinks for a short period of time and then begins to expand. The expansion continues at a steadily declining rate for a long period of time.
The instructions associated with the casting and measurements of Cerrosafe castings are usually vague and misleading. The chart that supposedly determine the actual value of the contraction and expansion values that is usually supplied with the casting material was copied from and old specification sheet that provided values measured at various time intervals . These measured values were then to be subtracted from the Squared dimensions of a 1/2" x 1/2" x 6" casting . The Square Root of the resulting sum was then taken to determine the actual dimension of the chamber one hour after the casting was made.
Of course, these values are meaningless when applied to a casting with dimensions that are either larger or smaller than 1/2" x 1/2" x 6" casting, as the contraction and expansion coefficients at the various time intervals are the result of ratios applied to the measured dimensions of the castings.
Experimentation has shown that measured values of the casting taken at about 1 hour and 20 minutes after casting will return actual chamber dimensions and that the casting will continue to expand at an ever declining rate thereafter.
The algorithm depicted on the Precision Cast Bullet Alloy Calculation software will return reasonably accurate values for the radial and short linear dimensions of the chamber by substituting the hours since casting and the measured value of the casting at that time.
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