Bringing the Lee Hardness Tester into the digital age

[Hal]

I had a chance to try mashing some minies this weekend and was surprised at the result. These dropped at .576" and I sized three of them down to .575". There was a distinct difference in how much they mashed under the same force. I was unable to make the Lee Hardness Tester work for this application, so I put the lower end of the minie under an ammo can with some lead in it and gently lowered it onto the bullets one by one ensuring I put the bullet underneath the edge of the ammo can the same amount each time. After mashing them, the three UN-sized bullets measured .522, .531, and .528, averaging .527". The three Sized bullets measured .540, .531, and .536, averaging .536". In other words, using the same force to flatten sized and un-sized minies resulted in unsized bullets flattening more than sized ones. So it would appear that sizing a bullet even .001" results in some work hardening that decreased the amount a given force would distort the skirt.

I will say this is in direct contrast to something I read on the Cast Boolits website many years ago which said that lead work SOFTENS rather than work HARDENING. I now tend to believe that was incorrect.

[John Holland]

The Old Wives Tale about lead "Work Softening" just won't go away! I believe that the Civil War Minnies that were produced by power swaging into a die were work hardened. I say this because nearly all original Minnies found on the battlefields and camp sites as "Drops" never have deformed skirts, even after 150+ years of being plowed up in fields, dug in camp sites, etc.

[Hal]

John,

Based on my experiment, I would have to agree. All I did was size them down .001" and could tell they had hardened. I would suspect a swaging operation would do even more hardening.

[Kevin Tinny]

Hello:

With the inherent inaccuracies involved in mechanically trying to definitatively determine age hardening of pure lead, either as-cast, chilled or swaged, it seems to me that someone will have to access one of those modern x-ray-fluoroscent spectrometer handheld "guns" commonly used in metals re-cycling/smelting facilities. I have seen them used and they are flat-out amazing. Verryy expensive!

They show alloy components to .01% and hardness. Just hold the minie to the window and the screen shows details. No guess work.

Respectfully,
Kevin Tinny

[Michael Bodner]

So, what about the depth of the hardness? By this I mean: Lee states that you should file a nice big flat spot on the bullet before using their tester. Is hardness in lead like that some heat-hardened steel in that it starts at the surface, or is it homogenous and you will get the same reading?


NOTE: Steel hardened in an oven get homogenous hardening. Case hardening (as I'm referring to above) starts at the surface and you can 'get through it' to the soft steel underneath.

Thoughts?

-Mike

[Kevin Tinny]

Hello, again:

Sorry to seem to be contradictory, but .... and with respect:

As it pertains to lead being "work/strain" hardened during swaging or SIZING:

Got out my trusty copy of CAST BULLETS by Col. E. H. Harrison,USA, (ret) NRA 1979.
On page 128 is part of a long article by Dennis Marshall, a lead metallurgist and avid cast bullet shooter, entitled: STRONGER BULLETS WITH LESS ALLOY. On 128, Dennis presents the topic of LEAD WORK HARDENING. He clearly relates in detail that lead, either pure or alloy work SOFTENS at room temperature. Lots of scientific and simple details are included to show WHY this is true. Yes, sizing DOES impart a bit of hardening, BUT IT DISSIPATES "spontaneously" IN TEN MINUTES AT ROOM TEMP.

I Googled "Does lead work harden" and found several scientific and "Castboolets" commentary that agree with Dennis.

So, yes, a test of a sized lead bullet might present a little harder reading if immediately measured, but the bullet will return to the original hardness in a few minutes.

By the time one gets to the range with sized minie's, they are back to original hardness.
Thus, sizing dies not create hardness that would matter in our shooting.

Respectfully,
Kevin Tinny

[John Bly]

The reason that lead self anneals or softens at room temperature is that it is above what is called the critical temperature. A comparison in steel would be steel at red heat or about 1500 Deg F. Steel is soft at that temperature and easily formed, the same as lead at room temp. Metals can have drastically different characteristics. An extreme example is mercury which is molten at room temp.