Dimples on receiver and bolt

[INLAND44]

That's it - verification of hardness with a punch. I have no idea how they controlled that process unless they had a machine for it. I mean, how do you hit a punch with a certain diameter, hardness and tip shape with a hammer, to deliver an exact and repeatable force? To do that by hand is impossible, but perhaps it didn't need to be as technical as I'm trying to make it. Maybe you just take a center punch and ball peen hammer and give the object a medium shot, not like you're trying to drive the punch through it. After doing a few hundred bolts, I imagine you would see and feel a difference if you hit a 'soft' one.

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[Patrick Chadwick]

I mean, how do you hit a punch with a certain diameter, hardness and tip shape with a hammer, to deliver an exact and repeatable force?

With a specialist machine, as you guessed. A local gunsmith, who is also a qualified toolmaker, even has one!

Here are some examples:
http://www.hardnesstesters.com/Products/index.aspx