Lee Hardness Tester re-calibration

[mehavey]

Anyone else run into this?

I picked up a Lee Hardness Tester 6-8 weeks ago, did a quick trial to figure out how to set up the microscope/prepare the samples/run the process using an adjustable microscope stand for steadiness/strong quartering light for impression dimple edge sharpness... then put it away.

I hauled it out tonight after last week's casting session w/ a new Paul Jones 45 Creedmore mould and one from Hoch using two RotoMetal-supplied alloys: Lyman #2 and 1-to-30.

First sample was a Lyman#2 bullet (with filed-flat surface), 30 seconds in the press and under the microscope it went: Dead on 0.059" dimple diameter for a BHN of 14.9 -- Great (!)
http://www.frfrogspad.com/miscellm.htm#Brinell

Then the 1:30 alloy: 0.093" diameter --> BHN 5.8 (Huh? it's supposed to be 9)
So... another 1:30 bullet and another test: 0.094" --> BHN 5.7 (!!!??)

But before I call RotoMetals to yell & scream, I go out to the garage and pick out a pure (really pure) lead paper patch cast-off bullet from a session two years ago.

Another test: Pure Lead: 0.120" diameter ...and literally off the Lee reference scale. Something's wrong.

So I do a simple straight-line projection between the Lyman#2/0.059"/14.9BHN point (which I hope is right)
and the PureLead/0.120"/5.0BHN which I know is right
to get the following:


Lo and behold, the 1:30 alloy is now exactly where it belongs.



Have I missed something here?

.

[captaint]

While I can't say for sure, as I don't own a Lee tester, based on what you've done - it looks good to me. Go forth. enjoy Mike

[Plinkster]

Yep it's just for comparison and to make sure my boolits are consistent from batch to batch. I only really look at the dimple diameter and use the chart as a ballpark number, seems to work for me.

[montana_charlie]

You are not seeing aliens.
You now have 'good readings' because you made a chart that makes your tester agree with what you think is right ... not a chart which tells you what the tester is telling you to think.

I have your email address (somewhere) so I will send you a chart that takes readings down below 5 BHN.

Your results with the Lyman #2 prove that your tester is calibrated correctly.
The confusion with the 30-1 alloy stems from the fact that you are relying on 'the standard tables' to find out what 30-1 is 'supposed' to be ... and what pure lead is 'supposed' to be.
Those tables contain 'derived data', and they are wrong ... have been wrong for decades.

I don't know a 'good hardness number' for 30-1 because ... well, just because.
But I know that 20-1 is actually 7.8 BHN ... not the 10 BHN shown in the tables.
That should give you an inkling of how far off they are.
Really pure lead CAN test as soft as 4 BHN, but 4.5 is more common.


Lyman #2 data wasn't around back in the old days when the tables were published. That alloy was developed (and hardness tested) by Lyman long after the tables came into existence.
So, that 15 BHN was the result of actual testing of that alloy ... not derived from results in other tests where 'expert guessing' was used to calculate for alloys that were not actually tested.

I'll get that chart off to you ...

CM

[mehavey]

Here's (one) of my problems with the theory that 1:30 is extremely soft: Even using the references shown in Wayne McLerran's excellent article where the extended LEE/BHN chart is included, I still get the pure lead BHN measuremnts at/below 4.0, and the 30:1 measurements showing BHN ~5.6

By all accounts (and Lee's classic calculations) that's only good for chamber pressures ~ 7,500psi. Yet even black powder pressures in the 45 caliber cartridges are at least 2-3 times that and shooters still swear by 30:1.

Thoughts ?

p.s. I've got both #2 and 30:1, and could convert back and forth w/o any problem. I'm just (more than) curious at this point.
p.p.s. I've also got a couple of 20:1 ingots I cast out probably 10 years ago. I'll go try that out as well.
(My wife really didn't need the garage cleaned up any time soon anyway.)

[Chicken Thief]

Here's (one) of my problems with the theory that 1:30 is extremely soft: Even using the references shown in Wayne McLerran's excellent article where the extended LEE/BHN chart is included, I still get the pure lead BHN measuremnts at/below 4.0, and the 30:1 measurements showing BHN ~5.6

By all accounts (and Lee's classic calculations) that's only good for chamber pressures ~ 7,500psi. Yet even black powder pressures in the 45 caliber cartridges are at least 2-3 times that and shooters still swear by 30:1.

Thoughts ?

p.s. I've got both #2 and 30:1, and could convert back and forth w/o any problem. I'm just (more than) curious at this point.
p.p.s. I've also got a couple of 20:1 ingots I cast out probably 10 years ago. I'll go try that out as well.
(My wife really didn't need the garage cleaned up any time soon anyway.)

That Sir is the pressure where the alloy will start to obturate, not the max pressure it can be launched by!!!

[mehavey]

"...the pressure where the alloy will start to obturate, not the max pressure it can be launched by..."

I went back to my cy of Lee's "Modern Reloading" 2nd ed and re-read pp 104-110. In it Lee reiterates that "Chamber pressure must be less than the ultimate compressive strength of the cast bullet... select a load with the pressure equal to or less than the maximum pressure listed in the fourth column of the table."


Note also that Lee says "...best accuracy is obtained when peak chamber pressure is 10% LESS that the ultimate compressive strength of the bullet" "Chamber pressure should be ≥ the elastic limit [of the alloy] but less than the ultimate compressive strength... pushing the bullet hard enough to slightly [obdurate], ... but not so much that it wedges tightly in the bore [beyond its compressive strength] to cause leading."

Now if you're with me so far, here's the real kicker: "Lead that indents to 0.094 diameter or larger should be suitable for black powder guns." (p. 107) That 0.093/0.093 number equates to exactly my 30:1 tests and a BHN of 5.8, and a working chamber pressure recommendation of approximately 7,5000psi.

So where are BPCR chamber pressures in all this?

[montana_charlie]

So where are BPCR chamber pressures in all this?

As one example, the Pedersoli 1874 Sharps is warranted to operate with chamber pressure of 29,007 C.U.P. / P.S.I. (copied from the manual).
As far as I know, CUP and PSI are two entirely different animals, and there is no conversion formula that will accurately turn one into the other.

So, I load ammo that uses 'normal' components which will operate within 'normal' Sharps rifle limits, and just let terms like 'ultimate compressive strength' remain a mystery to me.

The Sharps rifle company considered 20-1 and 16-1 alloys to be entirely suitable for use in their rifles. With no desire to use propellants that can overpressure a Sharps rifle, I am content to follow their lead.
However, when it comes to testing alloy for hardness, I an VERY interested in knowing that my tester is giving me correct data, so that I can actually recognize that 20-1 when I come across it.

CM

[mehavey]

I'm beginning to believe you.

I actually ran the calculations in Excel after converting units, and in the process came to appreciation that BHN wasn't a measurement. It was a definition wherein everything is a constant except the depression caused by the ball. Period. There's no "reference" hardness. There's just the constant diameter Ball that causes the depression; the constant Force used to make it happen; and the resultant Depression itself.

And if the spring constant is correct, it will give you a BHN of 15 for the only true reference point: Lyman #2. At that point, everything else is automatic.

End of discussion.



All the lines are actual measurements (the WW ingot was from 8-10 years ago in my lead pile) .
And you're right.
Don't trust anything in any chart anywhere as to any Brinell hardness for most any material at this point.


Next... we'll talk about something less controversial: the best engine oil for classic British motorcycles

[whisler]

"Next... we'll talk about something less controversial: the best engine oil for classic British motorcycles"

Castrol!!!!

[montana_charlie]

There's no "reference" hardness. There's just the constant diameter Ball that causes the depression; the constant Force used to make it happen; and the resultant Depression itself.

And if the spring constant is correct, it will give you a BHN of 15 for the only true reference point: Lyman #2. At that point, everything else is automatic.

I believe you have caught on.

The difference between the Lee tool and the others is ... the Lee makes an impression according to the Brinell method, and the hardness is calculated from the dimension of the impression using the Brinell formula.

The others have a scale and pointer, or a reference chart, that is based on the BHN numbers found in the (old) published tables. While they are easy to use, and they are fine for showing relative hardness differences between samples, they don't 'calculate Brinell Hardness Numbers'.

CM