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When it comes to choice of tool steels, high speed is a normal fine choice. Taps for general use are carbon steel, and super duty taps are high cobalt high speed.
The high speed varieties can't go soft when heated by hard running (like milling cutters), but can't be tempered to a softer state of lesser brittleness to use for anything other than cutting or punching tools.
Every single factory-made firing pin that I have ever seen could be cut with a file, but no high speed tap will pass the file test. Some lesser metals are used to make firing pins, and the deformation mentioned earlier here is an obvious clue that the material was not able to withstand the deformity.
That does not mean that a non-deformable metal is better, just one that resists most deformity, but can give, just a little. Small peen deformity over time is to be expected, but large deformity is to be avoided. No deformity normally means hard to the point of brittle, just like a tap. A typical long firing pin can be bent somewhat into a deformed contour without breaking. No tap can be bent without cracking off, instead of deforming.
The drill shank is no proper metal for ensuring long life, since it can be much softer than the cutting area of the flutes, in many cases, and may not have been hardened at all, in the first place. Shanks can be capable of bending and sacrificing themselves rather than shattering, you know, injury reduction and all that. Not all bits have soft ends, the same as milling cutters or reamers, some soft shank, some hard to the end. In other words, scrap tool parts have too many variations to make any sure and valid choices that are far removed from the original metal's function.
I have reworked broken milling cutters and center drills into specialized one-off cutting tools or stub prick punches, as long as the bit I was using was hard. So, use hard left-overs to make hard newbies, not try to save a few nickels to make something else.
Heat treating mentions of hardening temps and so forth got me to wondering whether or not anyone here understands how a particular temperature got chosen. Do you think that the 1475 degree line (in one instance) could be the lowest temp. before any possibility of hardening is possible? There is a built-in fudge factor for the matter of maneuvering the parts from the oven to the quench line, variations in part thickness, etc. The temp. is supposed to be above the min. temp., but not so high that any danger of burning the steel (to the point of excess grain growth) destroys the strength potential.
Proper lab heat treat and temper, or double temper, are the best way to go, but sometimes practicality gets in the way by tripping over affordability.
If I was to give somebody a quick substitute material choice for a firing pin, and expect it to have workable results and decent lifespan, I'd say to use the shank of a high quality (preferably a grade 8) bolt. Something pretty hard, but machinable, but not brittle.
Remember to check my previous posts for a good overview from a gunsmith perspective.
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