Steel Hardness

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Weissen,
No hardness tester needed.
The most frequently used steel for Gun Barrels of that era was "1137 free machining steel", a very soft steel usually in the range in Rc 28 to Rc 34 which was the best condition for cutting very thin brittle chips which broke into small scraping like particles, Primarily due to the addition of 0.25 percent lead.
The toughness was comparable to hot rolled steel plate, or hot rolled structural steel, which happened to have much "rolled in scale inclusions", and thereby, very poor machining characteristics, as far as finish was concerned.
Because of the extremely small space available and small cuts allowed by such, the steels had to be of a variety that had a low resistance to cutter penetration and the production of very smooth surfaces without the need of polishing or lapping.
These quality was the basis for the formula of the steel to attain these qualities.
With the Post WW-2 discovery of Sintered Carbide tooling the use of single point and broaching methods rapidly changed to Button Rifling of barrels and allowed the use of higher strength steels of 3100 and 4100 series steels.
Luger barrels being basically of Pre WW-2 design were of the steels of the 1137 series characteristics.
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