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Thread: Tracking BHN of heat-treated COWW alloy over time

  1. #1
    Boolit Buddy
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    Tracking BHN of heat-treated COWW alloy over time

    Hey everyone--

    I'm trying to push the envelope on what's possible with heat treated, plain old clip-on wheel weight alloy, since I get it for free. I wanted to really carefully document my experiments so I could share them with the community and give back a bit. I just finished my first set of experiments, and learned a lot. I sat down to write up my results, and when I was done I had roughly 17 pages, which will definitely not fit into a forum post. So I have linked a PDF for anyone interested. Basically I was heat treating bullets at various temperatures and then tracking their BHN over time. The kicker is that all of this heat treating was done after powder coating, so I could find out if PCing interfered with the heat treat, or if the heat treat destroyed the powder coating. See page 12 for the actual data.

    Full write-up: https://drive.google.com/file/d/1zzZ...ew?usp=sharing

    TL;DR Version for those who have lives and don't want to read the whole thing:

    • You can powder coat, let the coat cool and cure, and then heat-treat up to at least 425 degrees for 90 minutes (where I maxed out) without ruining the coat (at least using Smoke's Clear PC). This gives you the advantages of a heat-treat/quench AND powder coat simultaneously.
    • My pure COWW alloy, at least, was able to get up into the high 20s for BHN using this method with 9mm projectiles. With .223 projectiles I was able to get up to nearly BHN 35. All of this is after powder coating.
    • My COWW alloy appears to get pretty close to stable hardness by the end of 7 days, but just to be safe, I'm going to continue giving bullets a full 14 days before shooting them. Your COWW may reach stable hardness sooner or later than mine based primarily on arsenic content. But I think I've confirmed, at least to my own satisfaction, that 14 days is a good universally safe amount of time to wait before loading/firing.
    • I have come up with a few more questions I want to answer through experimentation about heat treating and quenching--such as "does it matter how cold the bullets get when quenched, or just how fast the bullet temperature drops below a certain threshold?" It seems like one or both of those things changes your BHN after heat treating, since my smaller bullets got to higher BHNs with the same heat treatment as larger bullets.
    • The Lee hardness tester introduces some inherent human measurement error, particularly in the higher end of the BHN range it is capable of measuring. For future experiments, I'm going to be averaging at least 5 bullets for each "reading" to counteract that, as well as tracking standard deviation to help me know how confident I can be in my data. But 1 bullet per test just isn't enough for really useful results.



    Anyway, thought I'd share. More to come as I continue to tinker. Shout out to the guy who sold me his Lee tester for really cheap and made this possible. You know who you are, I'm just not sure you wanted me shouting your name on rooftops
    Currently in the process of developing the "perfect" cast .223 load for my AR-15. Click here to follow my progress

  2. #2
    Boolit Master popper's Avatar
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    Good test and write-up. Results similar to mine but I use a different (roto metals derived) alloy. IMHO you will get better results (higher BHN) with ice water as the cooling RATE really determines quenched hardness. The coating acts as an insulator, slightly slowing down the cooling rate. As your data shows, boolit MASS and water temp determine BHN. I don't have a BHN tester, just smash known (what works well in my gun) vs new in a vice and compare the 'flat' spot. She just gave me one of the floppy trivits so the plan is cook the PC (on hot plate) then re-cook in oven & quench. I also want to swipe one of her copper Yoshi cooking mats as a replacement for the NSAF.
    Whatever!

  3. #3
    Boolit Buddy
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    Thanks. I suspect you're right. I don't see how a minimum temperature at time of quenching would itself affect BHN directly. But quenching in ice water would cause the bullets to drop out of the high temp zone more quickly, which is almost definitely the mechanism determining final BHN.

    Honestly I don't think I need any harder, so no need to test ice water for me for now. I used 9mm bullets for the test because they were easy to crank out quickly in large quantities, and large enough to easily file a flat and test (compared to tiny .223 bullets that are just generally a pain to work with). In real life I don't harden my 9mm bullets, I just air cool, coat, and shoot. I only harden my Mosin and AR bullets for the time being, and even 24-25 BHN is plenty hard enough (possibly harder than I really want actually). I think it would be useful to be able to achieve any hardness in the range of 12-24 BHN as that would probably cover about 99% of any cast shooting I would ever do from any gun. Next test which is underway right now is testing some lower oven temps to see if I can get there. For now, water temp will remain the same.
    Currently in the process of developing the "perfect" cast .223 load for my AR-15. Click here to follow my progress

  4. #4
    Boolit Master

    Rcmaveric's Avatar
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    About 12bhn will cover 90% of anyones shooting.

    Sent from my SM-G925T using Tapatalk
    "Speak softly and carry a big stick; you will go far."
    ~Theodore Roosevelt~

  5. #5
    Boolit Buddy
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    Quote Originally Posted by Rcmaveric View Post
    About 12bhn will cover 90% of anyones shooting.

    Sent from my SM-G925T using Tapatalk
    Not mine
    Currently in the process of developing the "perfect" cast .223 load for my AR-15. Click here to follow my progress

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