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Thread: Warming up aluminum molds for heavy bullets

  1. #1
    Boolit Bub Rug480's Avatar
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    Warming up aluminum molds for heavy bullets

    Have a small setup and tried about everything save for a hot plate. Usually takes 14-18 castings to get my Mountainmolds 475-440 single cavity mold to reach temp.

    Tried dipping the corner, dipping the sprue plate tip, laying block inverted on the pot lip to heat the sprue plate first or slip a corner in lead with the sprue touching the pot lip to warm up both simultaneously. I would’ve thought it’d take fewer castings to warm up a 1x mold with such a big boolit. Just nature of the beast? Not a big deal, just a mild annoyance.
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  2. #2
    Boolit Master

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    Several things help and can be a benefit. 1) sit it on top of pot upside down while the lead melts and comes up to temp. A aluminum foils cover formed to fit over it helps hold heat in.
    2) dipping the front edge in the molten alloy may help but this may take longer than most think since the heat has to radiate thru the entire blocks mass. 3) The hot pate does good and may be the best method but it may still leave some bullets that are poor at the start. 4) when starting a mould out pour a larger than normal sprue, If possible cover most of the sprue plate with the hot lead. This helps to heat the plate and mould faster also.

    Some moulds take a little longer to run good bullets than others, some *** they break in and form the needed patina on surfaces cast better than when first new. It takes time and a little experimenting to learn what a mould likes wants and needs to run good.

  3. #3
    Boolit Bub Rug480's Avatar
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    Thanks gent, sound advice
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  4. #4
    Boolit Master
    Czech_too's Avatar
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    Before I got a hot plate and I dipped the whole bottom of the mould in the melt, I would hold it there until the lead no longer clung to the mould.
    In my mind, this told me that the mould was heated evenly throughout.

  5. #5
    Boolit Master
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    I got a hot plate from Walmart for 12.00. Leave it between low-med while lead is getting ready in pot. Works good from the start of casting session

  6. #6
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    I use a hotplate with a 1/4" plate of iron on top to heat my molds.
    Once you learn the proper setting for the hotplate the mold is up to temp by the time my Drip-o-matic has the melt up to temp.

  7. #7
    Boolit Master
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    I will preheat my H&G 8 & 10 cavity moulds on a gas stove on LOW heat. I put it on the stove while the pot is heating up.
    I have found that helps enormously. If I don't do that it takes 15 or more full casts to heat the mould.
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  8. #8
    Boolit Master RogerDat's Avatar
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    Hot plate with an inverted can over it. Notch cut in rim of can to make opening for handles to come out. Traps the heat and heats the mold from all sides. I also use the pour extra lead on the sprue plate to add heat. I ladle cast so that is an easy option. I just let the extra flow off the plate and back into the pot. I'll do that when casting if I sense the mold seems to be running cool.
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  9. #9
    Boolit Master redhawk0's Avatar
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    I have only LEE double cavity molds but what I've gotten into the habit of is, fill the mold and leave a large sprue puddle...then I leave it in that state for 30-45 seconds. I do this twice. The mold will then start throwing good bullets in about 2-4 more normal pours.

    I don't use a hotplate or dip my mold corners. This method has worked for me for 20 years.

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  10. #10
    Boolit Master

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    Sometimes the slower pace and added time allows the mould to pull more heat from the bullets and "normalize" faster. I have found you that a mould can be up to temp on a surface and cool on others. Untill it normalizes thru the blocks it may not do its best. Larger blocks with a single cavity may take longer for this to happen with out pre heating them

  11. #11
    Boolit Master Bazoo's Avatar
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    I normally set the mould at the top of my pot with the front edge of the blocks and the tip of the sprue plate in the lead. I leave it there several minutes. Sometimes I'll throw a cast into it first if the blocks want to open a little on the top of my pot. It brings it up past temperature, less the handles, I then let it cool a minute and start to cast slow until it evens out where I want it.

  12. #12
    Boolit Master

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    "...and tried about everything save for a hot plate." You've answered your own question. Get a hot plate! It is easy and gives you control. After all by casting into a cold mould you are pre-heating but in an awkward fashion.

    I use a two burner propane stove for casting (ladle caster) so use one burner with a piece of steel about 4" square x 3/6" thick to set my moulds on for pre-heating. you don;t want to overdo pre-heating and obviously you don't want to underdo it either as the point is to get the mould to casting temperature then cast. I pre-heat until the sprue plate lube just starts to smoke. This gives an even starting point each time and is a bit hot but easy to do and the mould settles in after a few pours so I can speed up but usable boolits come out from the first pour or two.

    A cheap electric hot plate will work but put a piece of steel on it rather than sitting your mould directly on the hot plate... especially aluminum moulds.

    Longbow

  13. #13
    Boolit Master
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    Quote Originally Posted by redhawk0 View Post
    I have only LEE double cavity molds but what I've gotten into the habit of is, fill the mold and leave a large sprue puddle...then I leave it in that state for 30-45 seconds. I do this twice. The mold will then start throwing good bullets in about 2-4 more normal pours.

    I don't use a hotplate or dip my mold corners. This method has worked for me for 20 years.

    redhawk
    Yep fill the mold and let it stand for a minute or two .

  14. #14
    Boolit Master Grmps's Avatar
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    You will find that every mold/firearm will have a "personality of its own". Keep a notebook and mark down what you try and what works best.

  15. #15
    Boolit Master

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    A propane torch works well for me. I place the mould on the lower shelf under my casting bench with a couple of ingots on the handle, mould block overhanging the edge, and the torch sits on the floor pointing up towards the block. I use a low setting and keep the flame about 2" from the mould.
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  16. #16
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    sometimes I'll move the sprue plate out of the way and cast directly into the cavities--and wait a bit

    then open the mold and all of the bullets will drop out as one if I ran a puddle of lead from one cav to the next

    I do that several times and I'll good to go
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  17. #17
    Boolit Master


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    with Lee molds I will just fill one cav several times, then two, then three, etc

    this makes cutting the sprue easier as you aren't having to cut all six at one time at the beginning when they cool very quickly and are hard to cut

    saves the handle on the sprue plate from breaking, too.
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  18. #18
    Boolit Master
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    Find a toaster oven at a garage sale they are cheap just leave the door open and put the mold in as far as you can. Works great been doing it for a while even when it's in the 30s in the garage.

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