Ideal hardness formula

[BBQJOE]

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?

[BBQJOE]

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.

[454PB]

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.

[leadman]

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.

[462]

Ignore any such formulae and your headache will instantly disappear.

[mdi]

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...

[45-70 Chevroner]

I bought the Lee manual for just that reason. I read it reread it, and read it again. I finally think I figured it out but so far I can't tell the difference in leading using the formula and doing what I have always done, (fit is King). I even bought the Lee hardness tester, because that is the one they suggested (daaah). The Lee manual is a good book but I could have lived with just the Lyman manual. I have spent money on a lot of things that are just hidden away some place. There is nothing like personal experience. [smilie=s:

[Larry Gibson]

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

[45-70 Chevroner]

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

[MtGun44]

Heard of it.

:coffee:

Bill

[44man]

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
This is something Larry and I have always agreed about. Neither of us likes "BHN" readings.
Pressure to lead alloy is like twist formulas.
Someone always publishes something that does not work and then others change the numbers to fit what they use, that makes the original formula useless. Now the changes are published to find it only worked for one boolit, one alloy and one gun.

[rintinglen]

If even that.
BHN times 1422 is the minimum presure required to obturate a boolit. IME, these "formulae" are more superstition than science, and serve absolutely no useful purpose. Except maybe to sell hardness testers, which, while of value to the manufacturer, is of darned little benefit to the rest of us.