Dan, here's the formula for BHN (the image is from ) :
- image005.gif (9.63 KiB) Viewed 14320 times
BHN = the Brinell hardness number
F = the imposed load in kg
D = the diameter of the spherical indenter in mm
Di = diameter of the resulting indenter impression in mm
The denominator in the formula is the spherical area of the indentation in square millimeters. Hopefully that makes it clear that a material's BHN number is the number of kilograms per square millimeter (kg/mm^2) needed to make the test indentation with the test indenter in that material. If we want pounds per square inch (lb/in^2), we can use 1 kilogram and 1 millimeter and substitute the appropriate pound/inch values to get the conversion factor:
1 kilogram = 2.2046+ pounds , 1 millimeter = 0.03937+ inches therefore
1 kilogram per square millimeter = 2.2046 / (0.03937 * 0.03937) pounds per square inch
= 2.2046 / .0015499969
= 1422.3254 pounds per square inch (lb/in^2)
with a little round off error.
30 BHN means "30 kilograms per square millimeter", and that really does represent applying a pressure of something over 42K pounds per square inch (which is the same as 30 kg/mm^2) to the tested material. Here are some numbers.
First in kilograms and millimeters
F = 27.2 kg , D = 4 mm , Di = 1.067 mm
BHN = 27.2 / ( ( 3.14159 / 2 ) * 4 * ( 4 - sqrt(16 - 1.138489) )
= 27.2 / 1.570795 * 4 * (4 - 3.8555)
= 27.2 / 1.570795 * 4 * 0.1445
= 27.2 / 0.90792
= 29.96 kilograms per square millimeter
And now the same dimensions expressed in pounds and inches
F = 60 lb , D = 5/32 = 0.15625 in , Di = .042 in
BHN = 60 / ( ( 3.14159 / 2 ) * .15625 * ( .15625 - sqrt(.0244 - .001764) )
= 60 / 1.570795 * .15625 * ( .15625 - .15045 )
= 60 / 1.570795 * .15625 * .0058
= 60 / .0014235
= 42149.63 pounds per square inch
There's round off error in all of those numbers, but I didn't feel like typing all the needed decimal places. The total error over both calculations is about one percent in the ratio of lb/in^2 to kg/mm^2.
None of that says anything about tensile strength. There is a relationship between BHN and ultimate tensile strength, but that relationship is material-dependent and involves the exponent of some test-dependent value in SomebodyOrOther's Law that I no longer remember and probably never understood anyway.
The primary point of my original note was simply that 1422 has a basis in reality: It's what's needed to convert BHN, which is expressed as kg/mm^2, into a number expressed as PSI. Lee wanted to do that so he could compare it with chamber pressure. Was there any real value in doing that? I have no idea. He claims he found some relationship between BHN_as_PSI, chamber pressure, and accuracy. You and the CBA say you've never seen such a relationship, barring the generally accepted belief that lowering pressure (within reason) produces better accuracy. Personally, I think you're correct that the real answer is to shoot bullets that fit correctly.