Does the mold & alloy temp affect bullet dimensions.
Example; mold running ~350, alloy ~690 verses a mold running 395 & alloy running 720. Assume it’s something easy to measure like a bore rider.
I’m talking about small difference. Like the difference between Linotype and #2 alloy. Maybe .0002 - .0003” on a 30 cal.
Thanks Bill C
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I wonder if mold temperature changes may create more dimension variation than alloy temperatures.
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I believe the numbers are so small as to be insignificant.
With rifle in hand, I confidently go forth into the darkness.
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I believe the numbers are so small as to be insignificant.
Pretty much agreed. Even #2 alloy to Linotype you can barely find .0002 and most casters can't measure to that level. And there’s a multitude of other things casters can do wrong that can affect bullet dimensions.
Personally I find that a hot, hot mold, with hot alloy will drop larger. Larger to the point that bullets won’t simply flop out of the cavity. And that’s measurable by bullet weight. A casting session with a hot mold (350) & hot alloy (710) may drop 209.0 +/- .1 where as a mold running 410 with alloy at 720 will drop at 211.0 +/- .1.
Are there 101 more important things to concentrate on for accuracy? Of course. I was asking a hypothetical question because the forum has been a little quiet lately. Thanks, Bill C.
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FWIW:
Last week I cast bullets for the 35 Whelen and the mould got hotter than I wanted and the bullets started frosting. Same alloy, same pot and within minutes of each other at the same temperature setting, 700*.
The frosted bullet nose is 0.3510" and the shiny nose is 0.3524".
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I think frostiness might be a different issue.
I have a DC #311041 that periodically lapses into frostiness.
My partially frosted bullets will always be on the light end of the weight spectrum, and this seems to come from the frostiness reducing the bullet dimension in the area of frosting
You are only as good as your library.
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Ric was that ladle pour? Did you notice any difference in the way they dropped out of the mold?
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Ric's example, the bullet cast at the higher temperature (thus frosty) being smaller in diameter, and Wilderness's being lighter, is the opposite of what we sometimes hear -- or what I thought I have heard.
It seems like bullets dropped out of molds of different temperatures would, after cooling, have a difference in diameters that would be a function of the difference of the coefficients of thermal expansion (shrinkage) between the mold material and the bullet alloy, assuming the the bullet and the mold cavity were identical just before bullet drop. This just occurred to me so I haven't tried to do the numbers. So it may be just a wild thought that may be flawed by a bad assumption.
John
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Ever measured the barometric pressure and entered it's variability into the cause for bullet sizing?
Dale Flinchum
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The thermal expansion of lead per degree Fahrenheit is approximately 16.02 x 10-6 or 0.000001602 inch. At 750 degrees, this will give approximately .0012015-inch expansion. With differing alloys and pot thermostats, you can use .001 by the time a bullet drops and cools. Also, the handling of the mold, how tight you squeeze each cast, operator fatigue, putting sprues immediately back in the pot, and the time of the casing rhythm can affect the diameter of the final product.
Experimenting with this scenario several years ago, I decided I did not have the equipment to perform a good experiment. The greatest factor I could control was the varying temperature range of the pot. I’ve gone to a PID controller to lower the range variation and work to keep the casting rhythm as repeatable as possible. The other factor I could control was casting rhythm. I now take a short break every twenty minutes. At this time I add back in the sprues and wait for the temperature to come back up.
I think the production mold companies do a good job satisfying the broad market. I bought double cavity molds hoping one cavity, if not both, would shoot well. My first RCBS 30-180-SP mold threw two slightly different bullets, one cavity shooting well in all .30 caliber rifles except one while the other cavity only shot well in my Springfield sporter.
I’ve now gone to chamber casts and custom molds for my competition rifles. My experimentation with a new mold is now finding the best temperature range for each individual mold.
Farm boy from Illinois, living in the magical Pacific Northwest
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Ladle poured with large sprue in a seasoned NOE AL three cavity mould.
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My theory is derived from Denis Marshal's article in the Lyman Cast Bullet Handbook" 3rd. ed. 1980.
Metallic solutions are only homogenous while above the temperature of the bi- and tri- metal compounds within the solutions. At any point you have a higher percentage of antimony than tin, you have the bimetal antimony/tin and free antimony. Antimony has a solidus point several hundred degree above the bimetal lead/tin.
When the mould is at elevated temperature, the free antimony will begin forming dendrite "tree" crystals. Those close to the edge of the cavity stop the flow of liquid lead/tin from reaching the side of the cavity. Thus, the solidified casting is small than when the cavity is colder and allows a free flow of lead/tin.
This mould is rated at 280 grains from whatever NOE used for a standard. Weight variance is about 1/2 grain between the two, or 0.0056%.
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