One other consideration we seldom think about buzz, is that even fluid steel is not a perfectly pure and homogeneous product. The chemistry and metallurgical qualities can and do vary between heats and even within the same heat. There are varying amounts of impurities and inclusions such as rolled-in scale. So the strength of two seemingly identical dents or bulges in exactly the same place and with identical wall thickness may not react the same to equal pressures. If you've ever drilled, tapped, or machined a piece of steel and suddenly hit a spot that took off the cutting edge or broke the tap, you know that you've encountered one of these hidden defects. This is why they proof test the barrels of brand new guns, either internally by the manufacturer, or in government proof houses.
