yodogsandman
Well-Known Member
Does anyone know of any long term hardness testing? I've never seen any results from any. Something that would show how heat treated bullets age soften over time in some timed increments?
Long Term Hardness Testing?
- Thread starter yodogsandman
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I did a 10 year test. I had a box of RCBS 35 200 heat treated to BHN 30 stored in a box all properly marked with alloy, date etc. I forgot all about them and discovered them while cleaning out under the bench. I thought wow these gotta be putty by now but they tested 26 BHN. So in 10 years they did age soften but not much.
yodogsandman
Well-Known Member
I once saw something, somewhere that showed just how fast HT'd bullets age softened, over less than a year I think, and then stayed at about the same BHN for quite a while. Could be attributed to lots of things. Variables or not, we could always "read into" any testing that's been done and available. Maybe the BHN differences are "close nuff" and not worth the bother?
Hoping someone knows of any testing done in say, one month increments and for over a few years.
Hoping someone knows of any testing done in say, one month increments and for over a few years.
I know Rick did testing to show that various hardness bullets in a string caused larger groups. If we use bullets all of the same age should they not be pretty similar in hardness?
A test would be interesting but the time frame makes it unlikely to be completed. Cast maybe 1000 bullets, heat treat all the same, and check hardness and shoot a couple groups every 2-4 months over the course of a decade.
A test would be interesting but the time frame makes it unlikely to be completed. Cast maybe 1000 bullets, heat treat all the same, and check hardness and shoot a couple groups every 2-4 months over the course of a decade.
Such a long running test could never yield results worth such an effort. We already know that heat treated Pb/Sb/Sn alloy will age soften given enough time. We already know that the age softening is rather slow. A logical assumption would be that the age softening would be similar to the heat treating. When oven heat treating most of the gain in hardness is in the first few days with further hardening much slower over the next week or two. Age softening I would think would be much the same in reverse with most of the softening in the first year or two and then much slower softening after that. Remember my 30 BHN oven heat treated alloy only softened 4 BHN in 10 years.
When heat treating a Pb/Sb alloy the percentage of Sb will dramatically effect the hardening time curve. A 2% Sb alloy will achieve final max hardness in from one to two weeks. A 5% Sb alloy will achieve it's max hardness in two to three days with possible minimal hardening after that. The percentage of Sn in the alloy will effect the max final BHN achieved with Sn at 5% and over. I think it would also be a reasonable assumption that higher percentages of Sn would also increase the rate of age softening in addition to limiting the max final BHN. My alloy in the 10 year test was 2% Sn added to CWW alloy.
As a side note, bullet casters refer quenching Pb/Sb alloys as hardening, the metals industry never refers to quenching a Pb/Sb alloy as hardening, it is always referred to as "strengthening".
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When heat treating a Pb/Sb alloy the percentage of Sb will dramatically effect the hardening time curve. A 2% Sb alloy will achieve final max hardness in from one to two weeks. A 5% Sb alloy will achieve it's max hardness in two to three days with possible minimal hardening after that. The percentage of Sn in the alloy will effect the max final BHN achieved with Sn at 5% and over. I think it would also be a reasonable assumption that higher percentages of Sn would also increase the rate of age softening in addition to limiting the max final BHN. My alloy in the 10 year test was 2% Sn added to CWW alloy.
As a side note, bullet casters refer quenching Pb/Sb alloys as hardening, the metals industry never refers to quenching a Pb/Sb alloy as hardening, it is always referred to as "strengthening".
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yodogsandman
Well-Known Member
I guess I was thinking about what happens between working up that perfect load of high velocity and accuracy and then the groups opening up a few months later with the same batch of bullets and with everything else being the same.
Guess this shows that I need one of those store bought, fast lead hardness testers over my cumbersome ball bearing and scale arrangement.
Guess this shows that I need one of those store bought, fast lead hardness testers over my cumbersome ball bearing and scale arrangement.
First thing to do is a test like Rick did. What happens to group size in your rifle, with your load, if BHn is 18,20,22, or whatever. Is there a specific BHn that shoots best or is there a range that works well?
Another way to get around this is to use a richer alloy that depends less on heat treat for hardness. The alloy will only get so soft even with time.
We also always have the opportunity to only heat treat what we know we will shoot in the next year. Keep the rest of the batch as cast and heat treat as you go. You can also re heat treat bullets if they do soften with time, unless they are lubed.
Another way to get around this is to use a richer alloy that depends less on heat treat for hardness. The alloy will only get so soft even with time.
We also always have the opportunity to only heat treat what we know we will shoot in the next year. Keep the rest of the batch as cast and heat treat as you go. You can also re heat treat bullets if they do soften with time, unless they are lubed.
