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Thread: Casting temperature question

  1. #1
    Boolit Buddy
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    Casting temperature question

    I semi recently got a pid and have discovered the world of both consistent temps as well as accurate measurement of said temps.
    Before i got this i was using a dial thermometer that went up to 750.

    Often i was casting at temps above what the dial would measure, and have recently figured out that it probably wasnt accurate at all considering i can spin the circle piece and with it moves the numbers.
    I was also casting with wheel weights with no additional tin. Never really had a problem with fillout or casting period, but now have also started using pewter lead alloys rather than high antimony alloys. Kinda stepped up my game in a few areas at once.


    All of the Above is what leads me to this question, its really just a search for knowledge rather than a solution to a problem.....

    Why is it often recomended to cast at the lowest temp that provides good fillout? Casting at higher temps can make frosted boolits, but they are said to shoot equally well, and when ive gotten frosty boolits i havent noticed any change in quality.
    Praise the Lord and pass the ammunition.

  2. #2
    Boolit Grand Master

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    I find the accurate repeatable temps help me repeat a casting session, if I know the mould works well at 700* then the next time its 700*. Closer temo swings also make for consistency in your casting. Its is a means to control variables that can and do affect casting.

    Casting at the lowest possible temps will gain in several things. 1) wait time is lowered speeding the procedure, 2) there is lower fumes emitted at lower temps, 3) The pot is a little more comfortable to work around, 4) with most pots the lowered temps equal less power used making it easier on the pocket and equipment

  3. #3
    Boolit Bub
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    I liked frosty boolits. When the temps get up my reject rate drops to almost nothing. I am switching to almost exclusively HP molds so the extra heat helps. I'm powder coating everything anyway.

    There are lots of pics here of some great, shiny boolits. That was my goal for a while but have changed my priorities.

  4. #4
    Boolit Master



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    Shiny boolits and brass look nice, but don’t have much effect on accuracy. It’s more of a personal pride thing.

  5. #5
    Boolit Master
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    Quote Originally Posted by F_L View Post
    I liked frosty boolits. When the temps get up my reject rate drops to almost nothing. I am switching to almost exclusively HP molds so the extra heat helps.
    Yep!

    Don
    NRA Certified Metallic Cartridge Reloading Instructor

  6. #6
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    JonB_in_Glencoe's Avatar
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    Mold temp is more important than alloy temp. But they are related. Rhythm or casting pace regulates the mold temp. Once you develop a good consistent rhythm, that is when you can dial your alloy temp down to where you are maintaining the correct mold temp for your casting rhythm.

    Some boolit casters have a temperature probe in the mold, NOE offers that option on all there molds. If you don't have that (most of us don't), then you can roughly gauge mold temp, by the color/condition of the boolit. "Shiny" is on the low side, and "coarsely frosty" is on the high side. The best is in the middle of those two conditions,which is the Goldilocks condition, "just right", that is a dull grey that isn't shiny and isn't coarsely frosty.
    ~~~~~~~~~~~~~~
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  7. #7
    Boolit Master
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    I set the PIDs on my 4-20 and ProMelt (the first feeds the second) to 720*. When my 8 cav aluminum molds are up to temperature, I get the most uniform boolits with the best fill out and virtually no rejects when they all have a very light matte frosted appearance.

    For me, shiney boolits mean too many rejects with wrinkles and poor fill out.

  8. #8
    Boolit Grand Master


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    I do not use a PID but use 2 thermometers in my Lyman Mag 20. One is just off the bottom of the pot measuring the temp of the bottom half. The other is half way down and measures the temp of the top half. I alloy the alloy, once melted and fluxed once to stew for 30 minutes +/- before fluxing a final time before casting.

    Measuring the alloy temperature in the top and bottom gives a constant reading of the alloy temperature. Most all furnaces do not have the heating element surrounding the entire pot. Thus the alloy is usually not heated evenly and as the alloy is used and the level goes down in the pot the alloy temp goes up. Lee's pots are world famous for this. The Lyman Mag20s heat element is around the bottom half of the pot. Thus with the thermometers monitoring the top and bottom half of the alloy I am able, by tweaking the temp knob, to maintain an even alloy temperature of 710 to 725 degrees regardless of the level of alloy in the pot.

    When I ladle pour I use the smaller 10 lb Lyman electric furnace. The short thermometer is used when the alloy first melts and when the alloy is up to 715 degrees I adjust the temp knob so it just shuts off. I let the alloy stew for 30 minutes and tweak the temp knob if necessary so the furnace temp adjustment keeps the alloy at that temp. I flux and begin casting. The smaller Lyman furnace does a good job of maintaining the alloy temp.

    Many do not realize just how fast the alloy cools between the furnace and the mould. It is imperative to have the alloy at a temp level hot enough so the alloy is still molten throughout the fill out of the mould cavity. Casting with the alloy just above the molten level can easily result in wrinkled bullets and/or incomplete fill out, especially if casting in cooler ambient temperatures such as in the garage during the winter. Keeping the sprue plate as close to the bottom pour spout as will allow a good sprue pour is best. With the ladle hold the mould right over the pot and lift the ladle out of the alloy and pour into the cavity as quick as possible. Then with all else working well maintain a sutable casting tempo.
    Last edited by Larry Gibson; 03-07-2020 at 01:13 PM.
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

  9. #9
    Boolit Buddy
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    Lee 4-20, PID with probe 1/2” off bottom. With a temp setting of 670, I can get the mold to frost just enough I don’t have to cool it. I will cool the sprue plate for about 1 sec on a damp towel every other cast or so to keep the speed up. I could probably go cooler and faster, but I don’t preheat ingots and that crashes the pot temp each time I add an ingot. If I heated the ingots, I could lower pot temp more and cast even faster.

    The lower you can keep your pot temperature, the faster you can go. You need to keep heat in the mold, and you do that with lots of lower temperature pours, or fewer higher temperature pours if you’re going slower and mold is cooling more between each cast.

  10. #10
    Boolit Master
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    Cast where you get good bullets and the mold likes it.IE no bad bullets.The mold drops well every time.The mold will tell you where it likes it.That said all depends on you doing your part.The PId just give you a constant lead temp the rest is up to you.Each different alloy will look different as they will cast at different temps. So yea no total solution using the PID.Just one less thing to worrie about in the whole process.

    Now thing that i have found to work for me just may not work for everyone.The less good tools you have the longer the learning curve.It took me a long time to learn what the mold was telling me no matter how many times i read it here i just had a hard time with it.Some cast with no help from and temp control or thermometer.yep sure can be done.some use methods to detemine there alloy wher it is the thumb nail scratch or if it thumps or rings maybe how there alloy cast.

    I have a Pid.I have a Lee 4-20 and a RCBS Pro Melt I have molds from several makers.I Get my lead tested for several reasons to be consistent and not using to much spencive alloy.Still like to mix alloy in big batches 300lbs at a time or so.After all that some days the casting gods are not smiling on me.So you just shut everything down and go find something else to do.

  11. #11
    Boolit Grand Master

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    Something I have not seen listed yet is oxides. It seem like you get more oxidation on your melt at hotter temps. I like to cast around 725º. Others differ.

  12. #12
    Boolit Buddy Tazlaw's Avatar
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    Tin will start to oxidize at 150*c or 302*F (per internet). So it seems to reason, the hotter the tin gets the more it will oxidize. Thus a lower casting temp keeps more tin in solution.
    Just knowing enough to do it, is not enough to do it right! -Taz

  13. #13
    Boolit Grand Master


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    Oxidation of alloy on top of a melt is not tin that is drawn out of the alloy. It is the alloy itself. Or, it is not tin that has separated from the alloy. The "oxidated" part will have the same composition of the alloy.....because it is the alloy. Oxidation on top of the melted alloy hurts or changes nothing.

    With my Mag20 with 18 lbs of #2 alloy after fluxing I start casting and put the previous sprue or reject bullets right back into the furnace while the next sprue is hardening. I keep the temp constant as previously mentioned and do not flux again until I'm done casting, the pot is almost empty with 4 +/- lbs left or I add more ingots for continued casting. Alloy composition remains consistent through the casting session. Again, the tin does not oxidize out of the alloy at normal casting temps. What is seen on top is simply oxidized alloy itself which is why it will flux right back in as the fluxing removes the oxide. And, no, this is not my theory but has been thoroughly tested by those who can analyze alloy.

    Also, as the alloy level drops in the furnace the pressure drops so the amount coming out of the spout will lessen. I adjust the spout opening as alloy is used out of the furnace to maintain the same flow out of the spout. When more alloy is added I close the spout opening.
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

  14. #14
    Boolit Master
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    Tons of great info above, so I'll be brief. As mentioned, it's the mold temp that matter, not the melt. The following are usually where I cast with my own natural cadence. It's also worth noting I beleive my PID reads about 30 degrees higher than actual temp. I'll list my PID temps. I also prefer aluminum molds.

    COWW normal pistol bullets - 720F
    COWW rifle, especially long/heavy - 740F
    Round ball- 700F
    Pure lead muzzleloader conicals- 820F

    Hopefully that gives you a general starting point.

  15. #15
    Boolit Buddy
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    Wow. Thanks for all the replies. I feel like i gained some insight.
    Praise the Lord and pass the ammunition.

  16. #16
    Boolit Grand Master

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    Wow, I've been casting about 30 years and I guess I'm lucky. I started with a Coleman stove and no exacting temperature measurements, but I made some good 44 caliber bullets for 18 months then got a bottom pour pot. I just varied the flame when I got frosted bullets or slowed down casting. If I got poor fill out or wrinkles I turned up the flame or sped up my cadence or heated the mold. Personally I don't believe it's necessary to know, within 5 degrees the temperature of my alloy and my eyes and micrometer are the deciding factors in deciding how hot my equipment needs to be. But lots of casters need to know exactly how hot their equipment is (PIDs and laser thermometers), just my experience without...
    My Anchor is holding fast!

  17. #17
    Boolit Buddy
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    Quote Originally Posted by mdi View Post
    Wow, I've been casting about 30 years and I guess I'm lucky. I started with a Coleman stove and no exacting temperature measurements, but I made some good 44 caliber bullets for 18 months then got a bottom pour pot. I just varied the flame when I got frosted bullets or slowed down casting. If I got poor fill out or wrinkles I turned up the flame or sped up my cadence or heated the mold. Personally I don't believe it's necessary to know, within 5 degrees the temperature of my alloy and my eyes and micrometer are the deciding factors in deciding how hot my equipment needs to be. But lots of casters need to know exactly how hot their equipment is (PIDs and laser thermometers), just my experience without...
    Yupper, lots of dead confederates and union boys done in with seat-of-the-pants castings.

  18. #18
    Boolit Grand Master popper's Avatar
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    Well, alloy temp does matter. If you get fine fins and smeared base cuts, too hot. If it flows like water, too hot. I didn't have a thermometer when I started, learned the hard way. I run my Al. moulds just on the frosted side. That is casting rate, not alloy temp. PIDs work great!
    Whatever!

  19. #19
    Boolit Master
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    I have a mold that is borderline for diameter in my 1911. Higher alloy casting temp produced SLIGHTLY smaller diameter bullets. Only .0003" but enough to cause leading. 725degF for the high and 675degF for the cooler. Liquidius for the 50/50 + 1% Sn is 587degF.

  20. #20
    Boolit Master
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    Quote Originally Posted by mdi View Post
    Wow, I've been casting about 30 years and I guess I'm lucky. I started with a Coleman stove and no exacting temperature measurements, but I made some good 44 caliber bullets for 18 months then got a bottom pour pot. I just varied the flame when I got frosted bullets or slowed down casting. If I got poor fill out or wrinkles I turned up the flame or sped up my cadence or heated the mold. Personally I don't believe it's necessary to know, within 5 degrees the temperature of my alloy and my eyes and micrometer are the deciding factors in deciding how hot my equipment needs to be. But lots of casters need to know exactly how hot their equipment is (PIDs and laser thermometers), just my experience without...
    I started without anything too. Casting is enough of an art as it is, I take consistency where I can get it.

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