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Thread: Questions about Casting Large Boolits

  1. #21
    Boolit Grand Master


    GregLaROCHE's Avatar
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    Quote Originally Posted by jethunter View Post
    I cast quite a lot of 500gr and 535gr for 45-70, and some .600" 530gr for Martinin Henry and haven't seen this issue before. The sprue is taking about 35 seconds to cool sufficiently with a fan which I think indicates a good mold temperature for a bullet this large, and pot temp is approaching 900F. In the past I've been able to solve these problems by going a higher temperature but not this time.

    Bullets aren't frosted or overly shiny, they look about right for this alloy.

    Has anyone enlarged sprue cutter holes for large volume bullets?
    I cast .45-70 500grains in a Lee mold. I know I get best results when lead and mould are hot. Just below frosting temperature. The mould gets too hot fast, so I cool it down on some wet rags or sponge often during casting.

    I was wondering about the time it takes for the sprue to cool? For me its 3 to 5 seconds when things are going well. Was your 35 seconds a typo or does it really take that long to cool? If so, I think your mold has gotten way too hot.

  2. #22
    Boolit Grand Master

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    One thing to offer here, If you decide to open the sprue holes up. Remove sprue plate from mould and set up flat in a vise. Lock down to drill press table centered. Find a pin pin 4" long that just fits in the chucks key hole. use a counter sink to cut the hole bigger. To avoid chatter and grabbing lower spindle into hole and turn by hand using the pin for a handle. Most drill press run to fast for heavy countersink operations. Using a bigger drill and opening the hole up leaves a web or flat on the sprue hole where it cuts making it harder to cut the sprue since your driving the flat and not a sharp edge. When the hole is opened up lay plate flat on a flat surface and sand paper and remove burr and any displaced metal

  3. #23
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    Quote Originally Posted by jethunter View Post
    I think you have something there, the cavity wall between the end of the nose and the outside of the mold is very thin.



    I cleaned the mold again and it was venting better today, also raised pot temp up to 900F. Still some bullets with small voids but most were good. I think I can improve my pouring technique and get 100%.

    Thanks to everyone.

    You could probably test it by keeping your alloy temp lower where you normally cast your heavy bullets then just rest the mould on a warm hot plate between pours. Keep that section warmer.
    I guess an armed thermometer could tell you how much temp you’re losing at that thin section too. It’s acting like the fins on a heat sink.

  4. #24
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    Run big molds hot and fast to get good fillout .opposite when using normal molds then I use 2or 3 molds at once to allow them to cool down before dropping boolits.

  5. #25
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    Quote Originally Posted by country gent View Post
    One thing to offer here, If you decide to open the sprue holes up. Remove sprue plate from mould and set up flat in a vise. Lock down to drill press table centered. Find a pin pin 4" long that just fits in the chucks key hole. use a counter sink to cut the hole bigger. To avoid chatter and grabbing lower spindle into hole and turn by hand using the pin for a handle. Most drill press run to fast for heavy countersink operations. Using a bigger drill and opening the hole up leaves a web or flat on the sprue hole where it cuts making it harder to cut the sprue since your driving the flat and not a sharp edge. When the hole is opened up lay plate flat on a flat surface and sand paper and remove burr and any displaced metal
    Makes sense. Good points, thanks.

  6. #26
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    Quote Originally Posted by GregLaROCHE View Post
    I cast .45-70 500grains in a Lee mold. I know I get best results when lead and mould are hot. Just below frosting temperature. The mould gets too hot fast, so I cool it down on some wet rags or sponge often during casting.

    I was wondering about the time it takes for the sprue to cool? For me its 3 to 5 seconds when things are going well. Was your 35 seconds a typo or does it really take that long to cool? If so, I think your mold has gotten way too hot.
    Is your Lee Mold a single cavity? They cool much faster than multi cavity molds.

    35 seconds is correct, for big bullets I've always needed to run high temps to get good fill-out and adjusted the cooling period accordingly. Bullets are not frosted.

  7. #27
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    Sounds like you are losing too much heat through the base of the mold. Keep it in the lead pot before pouring, and drop the pot temp back down to 725 deg or so.

  8. #28
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    Keeping the mould up to temp may be an issue if it is a thin section under the nose as has been said. I have seen sprue plates pull heat from the stream and cause issues. on a bottom piur pot this is harder to do but you might try over filling the sprue hole to almost cover the whole plate to keep everything up to temp. Check vent lines and clear carefully.

    I cast 550 grn 45s in brass mould with no issues but I ladle cast and don't pour a sprue but pour the whole ladle of lead into the cavity letting the excess run off and back into the pot.

    At 710 grns its going to empty a pot quick so dipping may work for a short time. An aluminum mould losses heat quickly and a thin section may act like fins on a air cooled cylinder. Steel moulds are better for holding temps and are heavier. Brass blocks heat evenly hold heat longer but can be a very heavy set of blocks. My brass moulds take almost twice as long to cool as the steel do at the nd of a session.

  9. #29
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    I cast some pretty big boolits for my .585 Hubel. 780 grain and 1150 grain and found that if I run the mold hot I have no problems with fill out or voids. My molds are mehanite for these and the biggest aluminum I have is only 500 grains but gives no such problems.

  10. #30
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    I actually increased the holes in my spure plate (Lee 440gr) for the same reason. Lee has made these with so little metal that it's virtually impossible to keep this mould at a "good" casting temp. I simply run it hot and accept the frosted ones. I powder coat them anyway.

    Motor

  11. #31
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    900 degrees? My pot barely reaches 750 degrees and as long as my mold is heated properly I have no issues. That melt has to pour quickly to retain temperature until filled out. Of course I'm only pouring 440 grain bullets in a 2 cavity mold. How many cavities is yours?
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  12. #32
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    Quote Originally Posted by Dieselhorses View Post
    900 degrees? My pot barely reaches 750 degrees and as long as my mold is heated properly I have no issues. That melt has to pour quickly to retain temperature until filled out. Of course I'm only pouring 440 grain bullets in a 2 cavity mold. How many cavities is yours?
    3 cavity

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check