After processing oils are removed, the case must be inspected. The physical dimensions are checked against engineering specifications. Some cases may be set aside for grain structure evaluation and/or micro-hardness testing.
This test requires the following:
- Sample cases are sectioned and the cut surfaces polished.
- The polished surface is etched in acid to define the grain boundaries.
- The average grain size is measured, using a microscope with a calibrated eyepiece.
- A hard, sharp point is pressed into the metal with a known amount of force, leaving a tiny, diamond-shaped impression.
- The metallurgist measures micro-hardness using a microscope. The dimensions of the impression are measured; the smaller the impression, the harder the brass.
Some cartridge cases are nickel plated for appearance and/or corrosion resistance. Cosmetic plating is performed after all heat treating is completed and usually accomplished after passing inspection.
Additional Online Courses
- What Every First Responding Officer Should Know About DNA Evidence
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