Optimum BHN = PSI / (1422 x .90)

Mitty38

Seeker of knowlege
I Know, I know, fit is more important then hardness, But....
Came across this ,in some old notes I found in a box reloading estate stuff. The fellow who made these notes (RIP) was from the looks of things, a long distance rifle shooter.
Is there anything to this formula? Could it be useful under certain circumstances?
Optimum BHN = PSI / (1422 x .90)
 

Brad

Administrator
Staff member
Sounds like a Richard Lee thing to me.

I don’t think there is a single mathematical formula that determines “optimal” BHn. For one thing that would require us to assume an optimal BHn existed.

Way too many variables here. Is the BHn due to heat treating? PC or traditional lube? Bullet design is a huge factor. Are we using a good lube? Low or high pressure load?

Balance everything just right and BHn becomes far less important than one thinks.
 

Rick

Moderator
Staff member
Dunno if Richard Lee had that in his book(s) or not. First I ever heard of it was decades ago in Handloader, forget the author offhand and I would need to go find the article to be sure but I would bet money the word "optimal" was not in the article. Perhaps in Lee's book but not Handloader. I think the basic idea of the formula has some merit if put into the proper perspective. It can give you rough idea of a starting point but in reality not much more than that. Key word there is "rough" idea. As was mentioned, there is an infinite number variables and any one of them much less a combination of them would dramatically change everything. It can be one of those interesting things to play around with but don't bet the farm on it.

EDIT to add: Also keep in mind there are many ways to achieve a given BHN, two completely different alloys can have the same BHN and perform completely differently under the same pressure.
 
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Mitty38

Seeker of knowlege
Now, you guys said there was no such thing as a stupid question.
Just thought I would ask.
Hey , my first face palm here. :cool:
But I divided the pressure or my favorite 38 spcl wad cutter load.
9600 cup by 1279.8 which is the multiple of the 2 parenthesized numbers and got 7 bhn. Which sounds reasonable as I have shoot 8 to 9 BHN in my 38 slow loads, with very good results. I just noticed it says psi, so That might change things a bit.
 
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F

freebullet

Guest
Used in the Lee hardness tester...
rps20200229_232658.jpg

It's does have some useful purpose. extra info not a bad thing. We can get a relative idea what it'll take to obturate up. But applying it as Lee intended don't rule.

Don't worry about the face Palm. You haven't lived until you ask questions that leave this group speechless.
 

Bret4207

Undesirable member in absentia, Northern NY
It's not a stupid question at all. Wouldn't it be wonderful if it was that simple though?
 

Ian

Notorious member
It's not a stupid question at all. Wouldn't it be wonderful if it was that simple though?
This.

Mitty, the relative "hardness" of alloy run in loads developing 90% of the alloy's ultimate compressive strength at peak pressure is an attempt to put something into a box that cannot be. Sure, you can follow the formula (yeah, same units matter, there is no relationship between cup ans psi) and it will work for you. Ish. For target shooting anyway.

Let me ask you this. According to the chart and readily available load data, you will need at leas 30K psi to make a hunting load for your .30-06. 10% more for alloy strength is about 33,000 psi. What bhn would that require and would you dare hunt with an alloy that hard?
 

CZ93X62

Official forum enigma
I have seen a variant of this formula in the dim distant past--perhaps it was in Handloader. Dunno.

BHn x 1,422 PSI = maximum pressure gradient for given alloy in a plain-based cast bullet

I guess 9mm, 40 S&W, and 10mm will need gas checked bullets if they are going to function the slides and feed reliably. Taracorp/hardball alloy (92/6/2) will just turn to mud in front of 30K-35K PSI. Let's just say that my experiences differ......markedly.
 
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Bret4207

Undesirable member in absentia, Northern NY
whatever it is it would be exceeded by 12-13grs. of red-dot according to the BHN 'chart'
Yup, and yet for years a lot of guys shot gazillions of rounds of cast using that load and alloys that probably never exceeded 14 or 15 Bhn and we got got results that the formula says couldn't possibly happen.
 

CZ93X62

Official forum enigma
You would think that fairy tales and barnyard fables were the sum and substance of cast bullet knowledge at times. Lyman tried, and largely succeeded in directing people into Not Too Much Trouble. Handloader magazine was an occasional big help, too. But it took the internet to allow shooters/reloaders/casters to efficiently compare notes and experiences, and from that collaboration arrive at more meaningful and science-based conclusions concerning this hobby field.