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Thread: How to tell if lead is contaminated with Zinc?

  1. #1
    Boolit Man
    Join Date
    Jul 2012
    Location
    Canada, Ontario, Durham region
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    132

    How to tell if lead is contaminated with Zinc?

    I was casting Tuesday & Wednesday with 4 new pieces of casting equipment so I didn’t have high hopes for success this time.
    1) New furnace, a RCBS ProMelt-2
    2) New mold, SAECO #955 4 cavity 255 grain for 45 Colt.
    3) New single element hot plate, to preheat & keep the heavy iron mold hot.
    4) Alloy metal - mystery metal of unknown lead composition.

    The problems I encountered in casting and with the cooled bullets:
    1) Of the thousand bullets cast all show frosted except for the wide base drive band it’s mostly shinny.
    2) A large percentage cast with a slightly rounded base edge.

    How would I be able to tell if the mystery alloy was contaminated with zinc?

    The new furnace was much slower to melt the lead than my old LEE Pro 20#. The Pro Melt-2 is 25# pot. That’s a 25 percent increase in metal weight to heat and melt.

    This casting session was the first time I’ve use a hot plate to preheat a mold. I put a 4”x8” thin 1/16” thick sheet of steel over the burner coil tube a heat spreader and ran the hot plate at a low #3 heat setting.

    I use a LEE lead hardness tester on all the 6 one pound ingots cast from the last inch of lead from the bottom of the furnace pot. BHN 8 is as low as the LEE reference chart goes and my measurements show the alloy is BHN 8 to estimated 7.8

    I was lowering the pot temp from a high 845* because at the high temp I couldn’t keep a sprue puddle on the cutter plate it rolled off like water.

    At ~720* I could keep a Lima bean sized puddle on each inlet hole, the puddle was usually connected to the next in one finger length strip.

    A random sample of as cast bullets averaged weight is 263.1 grains and diameter is .4559” to .4564”

    Next time I’ll try to cast at hotter temp to get more diameter shrinkage and lighter weight and use a known alloy instead of scrap.
    Last edited by greenjoytj; 09-15-2018 at 04:36 PM. Reason: Spelling

  2. #2
    Boolit Master RED BEAR's Avatar
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    outside richmond va
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    they tell me pour a little muriatic acid on them and if there is zinc it will fizz. if not nothing. i wouldn't use them without washing off acid. all i have ever used is coww and scrap.

  3. #3
    Boolit Master
    sutherpride59's Avatar
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    Im not sure how you would be getting frosting with such a low BHN being as the frosting come from the antimony. Either way frosting is a hot mold not a hot melt, I would turn the heat up to 800 and try again, also adding 2% Tin and make sure you have your spue plate a little loos so the base can get proper venting.

  4. #4
    Boolit Master

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    May 2015
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    That's not very hard alloy to have Zink in it .

  5. #5
    Boolit Master

    454PB's Avatar
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    Mar 2005
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    Helena, Mt.
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    Those symptoms could also be from a contaminated mould. Was it thoroughly degreased before use?
    You cannot discover new oceans unless you have the courage to lose sight of the shore

  6. #6
    Boolit Master
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    Mar 2016
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    Boise, Idaho
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    454 is probably nosing at the culprit.

  7. #7
    Boolit Man
    Join Date
    Jul 2012
    Location
    Canada, Ontario, Durham region
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    132
    I used a sprayed can of brake cleaner to clean the mold, I don’t know how to get it the mold any more clean or de-oiled.
    I’m getting lead sticking to the top of the mold even though I was lubing the mold top with a PAG 100 refrigerant lubricant ( just bought some Red Line 2-stroke full synthetic ester racing oil) applied with a Q-tip applicator. Now it’s been wiped with a heavy coat of KROIL to see if the lead smears will pop off if the oil can migrate underneath the lead.
    I was thinking if I had zinc contamination the bullets would be lighter than the 263grs I’m weighing.
    I suspect there is little to no tin in this alloy I suspect all the hardness is from antimony.
    I have some Rotometal 20:1 to test this mold on the next casting session.
    This SAECO 955 mold has a massive chunk of solid iron between the bullet nose and the mold base, it so big SAECO could have flipped it over and cut 2 more cavities between the alignment pins.
    The sprue cutter will swing open & close freely when the mold is cold but there is no up an down play between sprue cutter and the top of the mold block.
    Last edited by greenjoytj; 09-15-2018 at 04:41 PM.

  8. #8
    Boolit Master

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    Oct 2009
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    It does not sound like zinc but you could do the acid test to check. It could be a contaminated mold. Did you spray it and scrub it with a tooth brush and spray it again? My strongest suggestion is to increase the flow filling the mold. Your pot temperature of 720-730 should be about right but you should be able to form a full size sprue.

  9. #9
    Boolit Master
    sutherpride59's Avatar
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    I say take it to the extreme then back it down, kind of a proof of concept. Scrub the mold with hot water and dawn dish soap the blue kind 3 times, smoke the mold with a bic lighter or a match no candles, then turn the pot to full blast, put your mold on the stove top or hot plate to preheat, pour your melt as fast as you can, check your sprue plate for burrs. If it still doesn’t make good bullets then it’s time to try a new batch of lead. If you get good bullets you can back the heat off and figure out what heat you need your melt at to get good results. If you still need help you can PM me for my phone number and I can help you out. I’m not an expert but I bet we could figure it out.

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