BABore made a simple but accurate hardness tester.
It's a spring loaded ram and a 3/8" ball that fit on a reloading press. The concept is not new, but this one is very well executed and easy to use. A flat point bullet or an ingot is set in place and then the ram is raised until the witness marks line up. It should be held like that for 30 seconds. BABore calibrated the witness marks with a load cell to produce 200 pounds force.
The detent is then measured. I got pretty good results using calipers and a magnifying glass. BABore uses a machinists' optical comparitor which should give even better accuracy. I used a spreadsheet to convert the measurement to BHN.
Here are some results:
Heat treated mystery alloy, unknown age -- 22 - 26 BHN
different batch of heat treated mystery alloy -- 26
rough ingot of lino -- 17 to 18
air-cooled WW -- 12 to 13
unknown lead/tin alloy -- 4
pure lead bullet -- 4
Some store-bought testers use a small indenter and a small force. A small indenter makes it easier to measure small meplats, but a large indenter is more accurate. This tester's 3/8" ball and 200 pound force are very close to the "official" 10 mm ball and 100 kg. force that are recommend for soft metals, so it should give reliable readings, and it did. Even with the big ball, it was easy to measure 35 caliber flat point bullets.
A gentleman on another forum is using a drill press and a bathroom scale to measure bullet hardness. At first I laughed at his crude system but when you think about it, there's no reason that it can't be accurate. As mentioned before, the accuracy of some store bought testers is limited by their small ball and small force. The homebrew testers, using a larger ball and force, should actually be more accurate.