Rockwell hardness tester
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.