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Thread: Internal mold dimensions and size of dropped bullets?

  1. #1
    Boolit Mold
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    Internal mold dimensions and size of dropped bullets?

    I am thinking about making a mold. Does anyone know the formula or where to find the formula that determines what the cavity dimensions should be relative to the size of the as cast bullet? I plan on using cast iron. Thanks.

  2. #2
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    depends on the amount the alloy shrinks.
    alloys with more antimony shrink less.
    usually +.001 to .0015 is sufficient for a ww type alloy.

    you also have to factor in the rate at which your mold will enlarge as it gets hot.
    sometimes many home-cut molds have to be re-cut hot [at cast temp of 375-f] to get them just right.

  3. #3
    Boolit Mold
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    Quote Originally Posted by runfiverun View Post
    depends on the amount the alloy shrinks.
    alloys with more antimony shrink less.
    usually +.001 to .0015 is sufficient for a ww type alloy.

    you also have to factor in the rate at which your mold will enlarge as it gets hot.
    sometimes many home-cut molds have to be re-cut hot [at cast temp of 375-f] to get them just right.
    Thanks, I'll be using 2/6/92 hardball bullet alloy.

  4. #4
    Boolit Buddy
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    What caliber, weight and type of bullet? How much larger do you want the bullet over your intended sizing diameter?

  5. #5
    Boolit Mold
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    .40 cal 155gr round nose and .45 200gr round nose. I am using 2/6/92 and sizing to .401 and .452 respectively so if they were dropping as cast at .403 and .454 I think that would be good. Thanks.

  6. #6
    Boolit Buddy
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    My 40Cal molds are cut at .406....but I'm sizing to .402. So .405-.406.

    My 45Cal 200 grain bullet molds are cut to .457. Larger 45Cal 230 grain bullet molds need to be cut larger, .458-.459

  7. #7
    Boolit Mold
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    Thank you!

  8. #8
    Boolit Buddy TomAM's Avatar
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    I'd use .4058" for the 40 and .457" for the 45 using hardball in iron to achieve the diameters you want. It depends a bit upon the size of the iron block... The cavities will actually expand by about another thousandth at casting temperature, and hardball will shrink about .005".

  9. #9
    Boolit Master

    Tom Myers's Avatar
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    Quote Originally Posted by dsa View Post
    .I am thinking about making a mold. Does anyone know the formula or where to find the formula that determines what the cavity dimensions should be relative to the size of the as cast bullet? I plan on using cast iron. Thanks.
    Quote Originally Posted by dsa View Post
    .40 cal 155gr round nose and .45 200gr round nose. I am using 2/6/92 and sizing to .401 and .452 respectively so if they were dropping as cast at .403 and .454 I think that would be good. Thanks.
    There are several " material expansion and contraction coefficient factors " that may be combined to devise an algorithm that can be used to show the variances in bullet size as related to mold cavity size for different mold materials, mold casting temperature, alloy type and alloy casting temperature.

    The Precision Cast Bullet Design ~ Advanced and Professional software programs incorporates these factors in a Mold and Alloy Expansion application that works quite well.

    If interested, the Help file page for the Mold Cavity Dimension application explains the processes used in calculating the cavity dimensions and as cast bullet alloy dimensions

    Entering the mold material, casting alloy metal percentages and mold casting temperatures for your desired as-cast dimensions, the application returns these dimensions for the room temperature mold cavity dimensions for either cast iron or aluminum mold blocks. The application also displays the calculated as-cast bullet dimensions when using various common bullet casting alloys.

    When viewing the images, look at the lower right and find the window labeled "Mold cavity, room temperature, body cavity diameter" to find the suggested mold cavity dimension for each combination of mold cavity material and casting alloy when casting at the indicated Mold Casting Temperature.

    Also, when selecting a "Custom Alloy" as used in these images, ignore the Casting Alloy value entered in the top right hand edit window.

    Hope this helps.


    Cast Iron 0.403 as Cast Diameter





    Aluminum 0.403 as Cast Diameter




    Aluminum 0.454 as Cast Diameter




    Cast Iron 0.454 as Cast Diameter
    Respectfully,
    Tom Myers
    Precision Shooting Software


  10. #10
    Boolit Mold
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    Thanks guys! Mr. Myers that program looks like a valuable resource, thank you very much. Now it is time to get to work.

  11. #11
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    Tom's program is the bomb it is super professional and answers a million questions we never had before.

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