Bringing the Lee Hardness Tester into the digital age

[Maillemaker]

So a while back I started mixing up 1:20 tin:lead alloy for my Sharps, 'cause some folks said it was the thing to do.

I thought, "Gee, it would be nice to use wheel weights instead of tin, 'cause I have a lot of wheel weights and tin is expensive!"

So, I got one of those Lee Hardness Testers. According to the web, it is among the most accurate. Basically, it's a little pocket microscope that has some lines etched in it that correspond to .002" increments on whatever you are looking at. It's got a little spring-loaded dimple maker you put in a regular press.

Problem is, I could not hold the little microscope still to save my life. I found it almost impossible to count the number of tick marks to measure the dimple.

So, I 3D printed a nice stand for it. But in addition, I printed an adapter so that I could mount a cheap USB microscope to it. It does not fully view the entire scale of tick marks, but it works very well. Now I can gently ease the thing into position and count the tick marks on the screen with ease.

https://i.imgur.com/v0a81CNl.jpg
https://i.imgur.com/xUzAkLjl.jpg
https://i.imgur.com/VQIyAV4l.jpg

I'm not sure I'm getting great results just yet - my 1:20 alloy is measuring out for hardness like 1:30 alloy should, and I'm pretty certain about my alloy. Gotta do some more testing.

Steve

[Jim Barber]

Steve,

Great idea! When my brother and I are casting, we always test out the chunks first-- but we look like two monkeys having relations with a football. One of us shines a bright light on the chunk while criticizing the measurement-taker's poor skills with the microscope. Usually we trade places a couple times until one of us catches a glimpse of the elusive dimple & scale. It's always a debacle. Under no circumstances can you use the Lee Brinell Tester after drinking half a pot of coffee!

Cheers,

Jim B.
Grove City, OH

[Maillemaker]

LOL Jim great visual! :)

Steve

[Chris Sweeney]

The Lee tester works well but it is super technique-sensitive! I get 1/2 point differences on different measurements of the same ingot. The instructions want you to file a flat smooth area on your test piece - I always wondered if there wasn't a bit of work hardening going on . . .

[Hal]

It is my understanding that lead actually work SOFTENS, but yeah, maybe it does affect it somewhat. But then what happens when you size a bullet? I'm sure there is some minute affect, but probably negligible in the grand scheme of things.

[John Bly]

Like most metals, lead work hardens when squeezed, sized or hammered. However lead at room temperature is above the critical temperature which means it is self annealing over time. Alloying elements can change the characteristics of lead. I'm talking about the pure stuff we use for minies.

[Michael Bodner]

How much will hard lead harden over time? Does it peak-out in so many days?

[John Bly]

Pure lead and lead/tin alloys soften over time. Alloys with antimony have different characteristics that I'm not familiar with as I don't use them.
The following is by Dr. Glen E. Fryxell - From Ingot to Target, Chapter 3 - Alloy selection and Metallurgy

Metallurgy of the Cast Bullet

Lead-tin (Pb-Sn)
Which metals do we add to lead to make better bullet metal and why? The first and most obvious need here is to make the alloy harder, but there are other factors that play into this answer as well. Historically, tin was used because it was readily available in pure form, mixed easily with molten lead and contributed desirable properties to both the molten and solidified alloy (castability and hardness, respectively). Tin also increases the hardness of the alloy but does not interfere with the malleability of lead (a key point that we‘ll return to). Tin lowers the viscosity and surface tension of the molten alloy, allowing it to fill out the mould more effectively, resulting in a higher quality bullet. Tin is limited in its ability to harden lead, achieving a maximum hardness of about 16 BHN at 40% tin. These binary lead-tin alloys undergo slight to moderate age softening upon storage (1-2 BHN units), with the harder alloys undergoing more of a change than the softer alloys. The hardness of a binary lead-tin alloy generally stabilizes after about 2-3 weeks. Heat treating binary lead-tin alloys does not provide any change in hardness. At typical lead pot temperatures, lead and tin are infinitely miscible with one another, at the eutectic temperature (361o F) tin is still soluble to the tune of 19%, but at room temperature tin is still soluble in lead at the 2% level, meaning that as the bullet cools down there is significant precipitation of a tin-rich solid solution in the form of granules and needles in a matrix of lead-rich solid solution. It is important to recognize that tin is well mixed in the matrix and it hardens lead by making the matrix itself harder.

[John Bly]

Here's more than you probably need to know about antimony alloys.

Lead-antimony (Pb-Sb)
Antimony on the other hand hardens lead alloys much more efficiently, with only 1% antimony producing a BHN of 10 while it takes 5% tin to do the same, and it takes only 8% antimony to achieve a BHN of 16, as compared to 40% tin. The name "antimonial lead" refers to binary lead alloys with 1-6% antimony, with the higher antimony alloys (i.e. those with >1% antimony) commonly being called "hard lead" in industry. While antimony increases the hardness of lead, it does so by impairing its malleability. At typical lead-pot temperatures (ca. 700o F), antimony is only moderately soluble in lead alloys, and as the temperature drops, the solubility of antimony is markedly lower than that of tin. At the eutectic temperature for a binary lead-antimony alloy (484o F), only 3.5% antimony is soluble (note that this is 123o F hotter than of the tin eutectic temperature, but the antimony solubility is less than 1/5 that of tin). At room temperature the equilibrium solubility of antimony in lead is only 0.44%. The precipitated antimony appears as small rods, at the grain boundaries and within the grains themselves. Electron micrographs of lead-antimony alloys clearly show discrete particles of antimony surrounded by a matrix of lead-rich solid solution. In contrast to lead-tin alloys, lead-antimony alloys age harden, sometimes as much as 50% or more. When these alloys are air-cooled, some antimony is retained in the lead-rich matrix and as a result these alloys age-harden as this antimony continues to slowly precipitate. This usually takes 10-20 days to achieve full effect.

It is important to recognize the antimony hardens lead alloys by a fundamentally different mechanism than does tin. Antimony hardens the alloy by precipitation of a separate crystalline antimony phase, which reinforces the squishy plastic lead phase that’s in between the hard antimony crystals. These alloys tend to be brittle because the plastic (squishy) lead phase gets its hardness from the reinforcing hard antimony rods. As the matrix gets deformed the brittle antimony rods shear off and the soft metal fails. In the case of the lead-tin alloys, the tin is more uniformly distributed through out the matrix, making the matrix itself harder, so plastic deformation of the alloy is more uniform and progressive, not the slip/shear of lead-antimony alloys.

[ms3635v]

This is the lead tester that I use. It is very simple to use and very accurate.

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[Kevin Tinny]

Hello:

As it relates to lead and lead alloy cast bullet age hardening:

John Bly can walk the talk. He's my go-to person. I think we agree on the following.

The NRA's book: CAST BULLETS, by then American Rifleman Magazine Technical Editor, Col. E. H. Harrison, USA, Ret, has two authoritative pieces on this topic.

On its page 102 is "Lead Alloys Age-Harden" and on page 111 is a slightly corrected piece "Age-Hardening of Alloys".

These go into useful detail. The point for us that prefer pure lead is that either of age-HARDENING or age-SOFTENING of PURE lead is insignificant for bullet and minie ball shooting requirements.

What IS also important is in the page 111 piece:
AGE hardening does NOT occur in lead-tin alloys, but does when ANTIMONY is present.

SUPPLIEMENT NO. 1 to the BOOK contains a piece on page 12 entitled "FROM THE LOADING BENCH Soft Lead? A Better Way To Tell?"

In this two pager by Kenneth L.Walters, he shares that ONLY pure lead SOLIDIFIES at 621 degrees and how to observe this with a simple dial thermometer. He emphasizes that the 621 degree solidification shows PURE, but nothing more about composition if not pure. Chemically pure lead has a BHN of 4 and so-called "pure" plumbers lead can be 5BHN, either of which is fine for those wanting "shootable" PURE.

When these books were assembled, they were the best and most technically correct PRACTICAL guide for cast bullet shooters. Guru lead metallurgists, such as Dennis Marshall, collaborated with the NRA and also the CAST BULLET ASSOCIATION.

Regards,

Kevin Tinny

Edited for punctuation. Kevin

[Michael Bodner]

So the take away is:. 2-3 weeks if antimony.

Reason asked. I worked up a load for a Maynard and achieved great groups. Ammo used had been cast and sat for several weeks before using. Cast more rounds and shot them 2 days later and they were literally all over the target.

Will retest with those same rounds now that they have sat much longer...

[Kurt Lacko 7862]

Mike if you get in a jam and know your going to have to shoot freshly cast alloy bullets and cant wait for them to age harden you can always quench them in water right out of the mold. You will of course have to test them to make sure they haven't hardened past your regular aged bullets. Your mileage may vary.
Kurt

[Michael Bodner]

I had heard about the quenching approach and tried it out. It DID result in harder bullets earlier, but not sufficiently hard for that particular carbine (with very shallow grooves). BUT it shot a heck of alot better than 'fresh' non-aged bullets.

I re-tried bullets that had performed terribly (the day after casting) and now that 2+ weeks have passsed, they shot like gang-busters....

The truly ironic part about this whole investigation: Pre-retirement, casting would be done one day and many days or weeks later, the bullets would be shot. Now that I have time and my own shooting range, I cast one day and go shoot the next. Looks like I need to be WAY more patient, at least when it comes to hard-cast bullets.... LOL

BTW: This probably explains why my Henry stopped hitting the paper 2 years ago... I was re-working up a tighter load and after using my 'old' bullets, the new ones literally wouldn't even hit the paper at 100 yds. No matter what I did with the casting, they just came out too soft and wouldn't hit. I can't wait for the weather to clear and re-try those old bullets again and get back into the Henry Matches!!

-Boots

[Hal]

Cast from clip on wheel weights and do the water quenching. They will be WAY hard. Seems like 14-16 BHN, but don't hold me to that. I've done this for 30 caliber bullets and shoot them at 1800-2000 fps. They turn to dust when hitting my bullet trap. I seriously doubt you need them THAT hard, but I say it to show what CAN be done. Of course, you can mix pure lead in with the wheel weights and still water quench them and they will be softer than 100% wheel weights. Play around with the mixture until you get the hardness you desire. It's the antimony that does the quench hardening. Wheel weights have the antimony in them. Contrary to popular belief, you'd be hard pressed to find even a trace of tin in today's wheel weights. Costs too much.

[bobanderson]

When I first started shooting BPCRS, a friend suggested I quench from the mould to increase hardness and also the diameter of my bullets. This worked well until a metallurgist friend told me that quenching is a temporary effect and that the bullets will return to their original state over a short time.

This thread suggests that bullets "age harden" which is completely new to me. Is it possible that lead has an "at rest" (for lack of a better term) Rockwell value and the casting pouring and quenching simply moves the needle temporarily? As far as age hardening improving accuracy, I know that old bullets that have lost their "shine" shoot better. Does tarnish from storage give you a slightly tighter fit?

[John Bly]

Bob, if you read it again you will see that lead/tin bullets age soften while lead/antimony bullets age harden. Most of us cast bullets in the colder months and shoot them in the warmer months so our bullets have stabilized to whatever they will be.

[bobanderson]

Bob, if you read it again...

I really enjoy these posts that combine combine science along with real world shooter's experiences, so I follow them until they reach their logical end. I DIDN'T re-read the whole thread before my last post.

Thanks for squaring me away, John.

[Jim Barber]

An interesting aside that my dad pointed out to me a few years ago: when you perform the "scientific" test of trying to crush (or at least oval-ize) the base of a Minie to determine whether it's soft enough, you'll find it's much harder to squash a Minie that's been through the sizer than a fresh-cast, unsized bullet. Try it some time. Curious.

Cheers
Jim B.
Grove City, OH

[Hal]

I'm gonna have to try that. To keep things scientific, I think I will use my Lee Hardness Tester and maybe put a piece of steel between it and the bullet so it is not a point load, but will put the same force on both bullets. It will be this weekend before I would have a chance to do it and will also have to see if I have any unsized minies, so don't hold your breath on seeing my results, but it is an experiment I'd like to do.

[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.

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[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.