Zn/Cu alloy

Discussion in 'Alloys' started by popper, Jun 18, 2017.

  1. popper

    popper Active Member

    Test to see why BLL on PB doesn't work at higher fps. HiTek coated bases, then Bll. GCd BLL works, PB doesn't. Even have a couple sans GC to try. Not expecting a lot of accuracy but hopefully no gas cutting/leading.
     

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  2. popper

    popper Active Member

    Some more tests with 30/30 & soft alloy. 170gr PB base HiTek coated, Bll lubed (a couple 185GC bare too). 50 yds, first shots were 170PB coated base, did OK, then leading set in. Also a few 185GC with BLL shot OK. Fps in the 16-1800 range with 2400. My conclusion: the alloy works PCd or GC and HiTek base coat does it's job but alloy by itself strips/gas cuts. Confirms my thought that gas cutting will blow the BLL off soft alloy. Managed to 'accidentally' put one rnd between 2 touching 2x4s, bored through the edge on one and spit the dickens of the other. When they hit the berm - big cloud of dust - hard alloy makes just a small 'puff'. Leading isn't terrible but obvious. I'll up the Cu & Zn next batch to see if the alloy works a little better.
     

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  3. fiver

    fiver Well-Known Member

    I think you can bump the Zn if you don't have other stuff in the alloy up near 2 maybe 3%.
    I'm not sure how it's reacting to the Cu though.
    your gonna get to a point where your alloy temps are up real high and then finally see a sheeting action under the spout.
     
  4. popper

    popper Active Member

    In this heat & humidity my casting sessions are only long enough to get some good ones to test. Haven't really had any problems so far at normal temp, 725-740F. This stuff is sort of weird. Dropped one from the bench and got a ~0.050" flat spot. Threw a couple as hard as I could and only a 0.2" flat spot on the nose. Hmm?
     
  5. fiver

    fiver Well-Known Member

    that is odd.
    unless maybe the alloy isn't completely staying tied together.
    or the percentages are lower than expected.
     
  6. popper

    popper Active Member

    After my 2nd cup of coffee, I revisited the stress-strain curves. Yup, non-linear for low stress. Squishy at low psi, then hard up to plastic region, then shear failure. Adding the Zn should stiffen at intermediate psi, Cu should increase the plastic region - both (& Sb) will move the plastic region up in psi. BHN testers make a measurement at the plastic region so are not accurate at low and high BHN.
     
  7. fiver

    fiver Well-Known Member

    well that could explain some issues with the 40 earlier then.
    it would also confirm my suspicions of the alloy being a bit better with the addition of something else to it.
     

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