2007
John Song
San Francisco, CA
Outline of Objects: The electroformation technique is used for duplicating surface specimens. A master specimen is put into a tank with electrolytes to produce a negative replica on the surface of the master. By repeating the same process on the negative replica, a positive replica is duplicated with the same surface topography as the master specimen. NIST plans to use this technique for the production of SRM (standard reference material) standard casings to support ballistics measurements nationwide. In order to ensure that the SRM casings are produced with virtually the same surface topography including casing signatures of firing pin, breech face and ejector mark, it is necessary to test the decay factor of the duplication process, and design an optimum plan for the duplication of a large amount of SRM casings with maximum uniformity of surface topography. Brief Methodology: Two decay factors, called horizontal and vertical decay factor α and β, are defined and tested for this purpose. The horizontal decay factor α is defined for quantifying topography decay among specimens duplicated one after the other from the same negative replica. The vertical decay factor β is defined for quantifying topography decay among specimens produced from one generation to the next generation. Summary of Results: 26 replica casings are duplicated from the same master casing provided by the National Laboratory Center of the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF). 17 casings are duplicated from the same negative replica, and are used for the tests of the horizontal decay factor α. Nine casings are the positive replicas of nine generations from the same master, and are used for the tests of the vertical decay factor β. The NIST topography measurement system is used for correlation measurements of surface topography. The topography differences are quantified by the cross-correlation function maximum CCFmax. Initial tests have shown that the electroformation technique can duplicate replica casings with high fidelity of surface topography. Based on these tests, the horizontal and vertical decay factors are calculated as α = 0.016 % and β = 0.086 %. General Conclusions: Based on the horizontal and vertical decay factor, an optimum production plan is designed for the production of 256 SRM 2461 standard casings. It is expected that 256 SRM standard casings could be produced from the same master casing with CCFmax values higher than 95 %.