When do you know ?

[vrh]

Lead continues to harden to a certain point in age. One month it may show a BHN of 14. Three months later it may show the lead has increased to a BHN of 15.5.
So when do you know the true BHN of your lead?

[Wayne Smith]

How much precision do you need?? For what you are talking about it's not lead, it's a trinary alloy, or maybe quartnary. If it hardens that much you have antimony and possibly arsenic in there.

Without knowing the exact composition and having hardening over time schedule, it's guesswork at best.

We haven't even discussed the heat/cooling differential!

[Larry Gibson]

"So when do you know the true BHN of your lead?"

The alloys true BHN (pure "lead" doesn't harden) will be what it is at the time of use.

I really haven't found a measureable difference in performance between a 14 BHN and 15.5 BHN of the same alloy. Also if you are just relying on one measurement then a 1.5 BHN difference is probably meaningless. An average of 10 measurements of different bullets will give a much better surety of BHN. It will also give you an ES (Extreme Spread) of your BHN measurements. You may find that ES to be more than 1.5.

Bottom line is I wouldn't worry about it.

[JonB_in_Glencoe]

As Larry says, that amount of hardening isn't anything to worry about for reloading target shooting boolits.

But to answer your question in a different way (and I assume you are talking about a alloy with antimony in it), the rate of age hardening will vary with the amount of antimony and to a lesser amount, the actual temperatures of the Mold and boolit when it leaves the mold and the ambient air temperature...and also the size of the boolit, all will effect the rate of cooling, which I believe effects the rate of age hardening to a small extent. Also if you happen to have some trace amounts of Copper in your alloy, that supposedly will increase hardness many months or a year later.

Out of my own curiosity, when I'm using a lead alloy that I'm not 100 % sure what it is, I tend to take a few BHN measurements for each batch of boolits, to give me a better understanding of what might be in that alloy ...and while they can vary from batch to batch, I can tell you what I've found.

My COWW is about 10 BHN one hour after they are cast, in the next day or two, they are 11 BHN, they may climb one more point in the next two week...but after that, they stay about the same.

I have a large batch of cable end alloy (from auto battery cables). After an hour the boolits will be about 10BHN, the next day or two, are usually the same, at the two week mark have climbed to 13 or 14. The the weird thing is, I have measured them at 6 months or so, and they will be even harder, 15 and sometimes 16. I figure there is some other trace elements in there maybe Copper or Calcium?

I also have a 94-3-3 that was blended by another member. He blended it mostly from Range scrap that he had scanned, then used the alloy calculator to blend in linotype and Solder and such to achieve a near 94-3-3. According to the scan, the range scrap has about .25% copper, which I assume came from smelting jacketed bullets and trace amounts of copper leached into the alloy during smelting. Anyway, the BHN measured an hour after cast is 13. The next day or two is same. Two weeks later will will climb a point. Then at 6 months is may or may not have climbed another point to 15.

Disclaimer: I am not a metallurgist, this is just my uneducated opinion and experience using the Lee measuring tool.

[1988-4551]

I still consider myself a beginner at casting, have a handful of molds that cast accurate bullets but haven’t gotten a hardness tester yet. The book in the stickies section (the cast bullet handbook?) has a chapter on lead hardness that answers your question. On my phone so I can’t search it but maybe a member with a sharper memory recalls?

[Wayne Smith]

From Ingot to Target is the name of the downloadable book - and it is a book. It is in the sticky section, a free download and well worth it.