I have tests that go back about 10 years on dental lead. I have a lot of it from my dentist. and I have had guys send me samples.
The dental lead I have is between 11.5 and 12.5 BHN. It is the same as clamp on wheel weight. Two samples I received from other guys came out the same hardness.
I do show one sample and I don't know where I got it but it was tested in 2010. My notes say "fresh dental" at 9 to 9.5 BHN.
That leads me to tell guys that don't know about it that alloy will continue to harden. Over the course of a month or more alloy will change.
Where this comes as a problem is a guy like me that will cast 1000 bullets at a time and set them on the shelf. Later he goes back and wants to patch and size his bullets. this kind of thing will happen.
My paper patched lee 500 S&W bullet will behave properly at 6 to 7 BHN. the bullet above was 9 BHN.