"optimum" Brinell hardness & Missouri Bullets - WARNING - MATH !

[Bookworm]

I was perusing the Missouri Bullet Co. website, and came upon this is the "technical" section. They claim that there is a formula to calculate the correct BHN for a given load, if you know the CUP for that load. For those interested, here is the link -
http://www.missouribullet.com/technical.php

What it says, is that the formula for the correct BHN is "Optimum BHN = CUPS/ (1492 x .90)",
which is a longer way of saying

BHN = CUPS/1279.8

There is a published load on Hodgdons site, 200gr LRNFP with7.8gr Universal is 15,400 CUPS (and 1045fps from that barrel)

So, according to them, my load of 7.5gr Universal under a 200gr LRNFP needs a BHN of just under 12. I am shooting that load with a boolit that tests at that BHN, and getting a very small amount of lead at the forcing cone, but I think that's a forcing cone issue, not a load/lube/boolit issue. That will be a completely different thread.

Anyway, there is no explanation on the site about what that number (1422 x .90) represents. For all I know, they picked it off a price tag on a used fleece parka at the local resale shop.

My question is basically ..... uh.... really ?

- anybody familiar with this formula ? any idea from where it came ?
Anybody ever use it ?

What the heck does that number (1422 x .90) represent ? ?

Comments ?

[jgh4445]

The "correct BHN" to do what? It's one thing to penetrate paper, another to penetrate 8 inches into a PO'd Grizzly.

[Bookworm]

"optimum" according to them -

An optimally hard lead bullet is simply one which obturates at a given pressure sufficiently to seal the bore against the gases which would otherwise “cut through” the soft lead (called “gas-cutting”, forcing molten lead into your rifling. A bullet which is too hard won't obturate and seal the bore, because the gas pressure is insufficient to expand the base of the bullet. A bullet which is too soft at a given pressure will experience excessive base expansion and vaporization of the lead, causing leading.

cut and pasted from the page

[dragon813gt]

Lee has the same formula on their manual. At least I think it's the same formula. I know one is in there.

As to MBC. In reality they use a high BHN and hard lube to keep their product from being damaged during shipping. They can post whatever they want on their site. But that's the reality of why they do what they do. If they sold optimal cast bullets they would be a larger diameter, softer alloy and use a softer lube.

[C. Latch]

"optimum" according to them -

An optimally hard lead bullet is simply one which obturates at a given pressure sufficiently to seal the bore against the gases which would otherwise “cut through” the soft lead (called “gas-cutting”, forcing molten lead into your rifling. A bullet which is too hard won't obturate and seal the bore, because the gas pressure is insufficient to expand the base of the bullet. A bullet which is too soft at a given pressure will experience excessive base expansion and vaporization of the lead, causing leading.

cut and pasted from the page

Not a word in there about sizing.

See dragon's post above mine. I think your answer is there.

[mdi]

I read about and tried "The Formula" a few years ago. I went through all the mixing, testing BHN, and sizing, but the only part of that exercise of any worth was the sizing. I could not tell any difference with hot loads of one BHN (soft) to another (hard). But all my bullets are sized to fit the gun they will be used in, so I beat the leading problem that way, long ago...

[44man]

Figures!!!!. Too much works but my problem is make the boolit softer to "obturate."
If a boolit is .431 for a .430 groove why bump a boolit to .457 or whatever brass can take? If a barrel will take .430" to .432" just why would you make powder make them larger? Did they not fit?
Darn, forgot about expansion after pressure drop to seal skid. Happy days found well down the bore!
Hard boolits do not seal is another dork thing. Sorry, lead can not be made hard enough to not expand. I wish the hard boolit causes leading would go away.
How does a rivet head on a boolit work?

[Maven]

Bookworm, Your point has baffled others as well. Here's a quote by Joe Brennan (aka joe b.) from our archives, which attempts to explain "the math":

BHN and Pressure
A quick internet search shows dozens of sites where success in shooting cast bullets is equated with some relationship between the hardness of a bullet (BHN) and the chamber pressure in the gun.
One relationship is that BHN * 1422 should equal pressure.
Another is that pressure should be between BHN * 480 * 3 and BHN * 480 * 4.
The word "obturation" is often mentioned.
BHN is the ratio of: force applied to a ball in contact with the test material for a given time; to the area of the semi-spherical indentation in the test material made by the ball. Units are kilograms and mm squared. Converting to pound-feet units, we find that BHN * 1422 expresses the ratio in pounds and inches squared.
Now 1422 looks like the 1422 in the first relationship above, and like the 480 * 3 in the second relationship. (480 * 3 = 1440)
The BHN testing dimple/crater/indentation area in the test material and the force applied for a given time have nothing that I can imagine to do with peak or average or initial chamber pressure.
So the contention is that for a given pressure, if BHN is too low, something bad happens, (I can't find out what), and if BHN is too high the bullet won't obturate-gas leaks by and the gun leads.
Does anyone out there have any information or data supporting this?

[Tom W.]

Uhhhh......o.k.

[Bookworm]

Maven -
I appreciate the read. I read it 5 times, and it appears that 'joe b.' goes way around the bush to ask the same question I did.
He had different "magic numbers" than I, but the same question.

I understand that lead needs to be soft enough to "grab" the rifling as it goes down the bore, yet hard enough to not "strip" as it does so.
I even understand that there must exist some mathematical relationship between pressure and required lead hardness to not "strip" the lead onto the rifling. That relationship has to take into account the twist-to-bore-diameter ratio. The formula may or may not exist, and these "magic numbers" appear to be an attempt to make that formula work.
Apparently the formula doesn't really exist, or is not fully understood. Ballistics is about 50-50 science and black magic. I was looking for an easier way to develop loads.

Looks like it's back to the old trial and error. "load 'em, shoot 'em, clean 'em, repeat". Just means I have to shoot more.

What a shame...chuckle... never really liked math anyway.

[Maven]

Bookworm, I found joe b's response while looking for Steve Hurst's articles in the "Fouling Shot" (CBA). Hurst tried to explain the math and reasoning behind it in order to determine bullet BHN & pressure relationships. Unfortunately, those are old articles and Google wasn't much help.

[MSD MIke]

I have never had any luck with any commercial bullet. They have all leaded my guns even if the size is proper. I cast my own and life is good. The three obvious differences are soft COWW lead, soft lube and square bases. One day when I retire I will have the time research and test those differences individually. None of this matters unless bullets and throats are of proper size.

Thanks
Mike

[runfiverun]

even Richard LEE didn't explain it while he was explaining it in his book.

I just ignore it and do what I want, sometimes it don't work.
usually it does waay beyond what those figures say it won't.
it isn't because they ain't right but I believe it's because it don't work that way.
think about it, shove something in a hole and push on it, it might try to get shorter or whatever.
but what ultimate shape will it take [a cylinder] get your boolit pretty close to that shape and allow it to flow a little closer to that shape under launch.
and what happens.
you destroy less of the boolit or alter it's shape less towards the ultimate compressibility shape in a barrel.
thus being able to push it harder than normal without upsetting the balance.

okay now the alloy part.
did you know antimony crystals break down inside a lead alloy and allow the lead to flow easier under pressure?
think about that.
the uber hard alloy is actually able to slump easier under pressure.
combine that with areas of non support and throw in some rotation.

1422 X Bent = Jack..... on paper.

[Bookworm]

okay now the alloy part.
did you know antimony crystals break down inside a lead alloy and allow the lead to flow easier under pressure?
think about that.

Now that I did not know. It does explain, however, why Babbit Alloy is so high in antimony. I never really understood why it was so. I suppose I could have asked my sister (the metallurgical engineer), but I don't know if that was within her scope of work. I cannot tell you how much I have learned just reading on this site.

[Bookworm]

I have never had any luck with any commercial bullet... The three obvious differences are soft COWW lead, soft lube and square bases.... None of this matters unless bullets and throats are of proper size...
Mike

This is true. I was not having problems with a commercial bullet, I was just perusing the website. I was getting some leading on one side of the forcing cone, just at the entrance to the barrel. I believe the cylinder is out of line, causing the bullet to "clip" the barrel edge on the way into the forcing cone. I actually dug bullets out of the dirt and examined them to reinforce my suspicion.

My Super Blackhawk Hunter is on the Brown truck, even as I type. It's on it's merry way to Long Hunter in Amarillo to get a bit of work done, including reaming the forcing cone to 11° and opening the cylinder chambers. Hopefully it will be back, 'ere too long.

I miss it already.

[Harry O]

The 1422 number is an old one and is used in engineering all the time (converting Bhn from Kg/mm2 to lbs/in2). It closely predicts the yield point (or yield strength) of metals. Once you go over the psi number, the metal will NOT return to exactly the same shape as it started as. That means that when you go over that psi number in the chamber, the base will NOT return to its same shape when it leaves the muzzle. This may have an effect on accuracy, and may not.

It is not a be-all and end-all. The longer the excess pressure is applied (like in rifles), the more deformation there is. The higher the excess pressure is applied, the more deformation there is. I use that number as a starting point when I handload. That is one variable I don't have to worry about. I can increase it from there. Sometimes I can go a fair amount over. Sometimes not. I believe that is because of a number of variables I don't have much control over (such as barrel diameter, straightness, smoothness, chamber/throat dimension, consistency of the rifling width, etc).

Anyway, anyone who says it is BS is going against 75 to 100 years of engineers using it in the real world. Like most things in engineering, the equations are guidelines or strong suggestions. They are not the final word.

[Maven]

Good explanation, Harry O!

[44MAG#1]

"The 1422 number is an old one and is used in engineering all the time (converting Bhn from Kg/mm2 to lbs/in2)."

How do you that 1422 number to convert the pressure of a 44 Mag, for an example, to pressure to BHN. Let's say I want to use a load that suppose to generate 36,000 CUP.

I am sure Elmer Keith, Skeeter Skelton, Ray Thompson and a host of others used that formula in their casting and shooting.
They can't be wrong.

[Bookworm]

Harry O, what I think you are saying is that the "magic number" is a Constant. The same as pi is a Constant.
Also, the reason it isn't exact is the myriad variables with which it interacts. For instance, I ran a load with a CUP of 36000 through it, it came up with a ridiculous BHN of something like 26 .

Okay, I can accept that. It certainly clears up my original question.

It's more fun, however, to call it black magic....

[DougGuy]

If you have a Ruger SA revolver, in .44 or .45 caliber, and you shoot heavy for caliber boolits, alloy that is soft enough to scratch with a thumbnail works GREAT! What is this BHN12 or thereabouts? Soft lube like Felix, gas checks, this 50/50+2% alloy is a match made in heaven for a Ruger barrel. Nobody needs a formula, right here is the formula. Try it, and enjoy never having to clean a bore again..