Ideal hardness formula

Boolit Bub Join DateMar 2013LocationI challenge your middle of nowhere, and raise you 5.Posts46

This was located here: http://www.grantcunningham.com/blog_files/15e296c61415e831fecfe8fddcc1dc92-414.html

Ideal hardness in BHN = Pressure / 1,920
Maximum BHN = Pressure / 1,422

Anyone else use this?

Boolit Bub Join DateMar 2013LocationI challenge your middle of nowhere, and raise you 5.Posts46

No one here is aware of this formula?
I have now read it on a number of sites, but it confuses the daylights out of me.
According to lyman, my 240gr 6.0 Unique loaded cartridge produces 10,300 cpu.
This would give me a BHN of 5.3 or roughly pure lead?

I'm giving myself a headache.

I'm aware of it, but it is really just a theoretical formula and not of much use in the real world. If it were true, my .454 Casull boolits would turn to putty at 55 KPSI.

I seriously doubt that any experienced caster depends on the formula.

You cannot discover new oceans unless you have the courage to lose sight of the shore

This has been around for a long time. I have used it as a guide to match the velocity I want to the BHN of the alloy. If you are shooting higher velocity rifle loads and tried to use 5 BHN you would probably get miserable accuracy and leading. So you use the formula to determine how hard your alloy needs to be so it will give you the performance you are wanting.
Remember the fit is king. You can use a harder alloy than the formula says as long as it fits the gun properly. I only use 2 different hardness of alloy now and it works well. About 14 BHN and 22 BHN.
This formula is also used in the new Lee reloading book.

Ignore any such formulae and your headache will instantly disappear.

Cast and shot lead bullets for mebbe 15 years before I tried "The Formula". Too much trouble for the results I achieved (none?). For me and my guns bullet to gun fit is way more important...

The formula is over simplified.

BHN is only 50% of the "hardness" of a cast bullet. Malleability/elasticity, etc. (whatever you want to call it) is the other half. You can easily have 2 cast bullets of the same BHN but one can be brittle and the other malleable. One can be pushed with higher psi and it isn't the brittle one. A lot depends on the % content of the lead, animony, tin and copper in binary, ternary and 4 component (quadra ?) alloys. Also the formula does not take into account the accelleration rate before the max psi is reached. Slow burning powders accellerate slower for a given psi and most often a higher velocity.

Having pressure tested a lot of cast bullet loads in various cartridges I no longer even bother with calculating that formula as its answer is most often meaningless.

Larry Gibson

Boolit Master Join DateSep 2009LocationArizonaPosts727

Great read Larry, and I only had to read it once.

Heard of it.

Bill

If it was easy, anybody could do it.

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Abbreviations used in Reloading
Pointed Soft Point "Core Lokt"

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