Mold too hot - boolit small ???

[milkman]

I have seen it posted several times that if a mold gets too hot the boolits will cast small. I'm not looking for a fight, but that runs counter to my experience. I find that my smallest diameter and weight boolits are from a cool mold and as the mold gets hotter the diameter expands and the weight increases. I have seen expansion from a cool mold dropping at .3596 to the same mold hot dropping at .3672 and the boolit weight going up with diameter. The hotter the mold the larger the diameter. Measurements were made at the parting line.

I don't understand how a mold could cast smaller boolits as the metal in the mold expands. Again, NOT looking for a fight, just an explanation.

Milkman

[Oreo]

The mold expands, yes, however, so does the lead. Lead at 800° will be expanded more then lead at 600°. The 800° lead has more shrinking to do as it cools which can account for a smaller boolit. Alloy plays an important role as well though. Some alloys expand less at molten temps and perhaps that is affecting the result you are seeing.

[357shooter]

I've found that a hotter mould casts larger bullets, up until the point of frosting. At that point they are actually smaller, and the mould is now too hot. So mould temp just shy of frosting is best for full size bullets. The frosting effect or process somehow causes undersized bullets. I expect that it's from sucking in air from the vent lines instead of drawing lead in from the sprue. It doesn't really matter why, it just is the way it works. This is true for any alloy.

I usually cast with hot alloy, that is very soft. So 800 or hotter works for my current moulds, with alloys softer than WW. WW and harder (which I rarely cast) work with 750. These are all aluminum moulds using Lee six cavity blocks. The alloy and the mould material / blocks / bullet size all seem to have an impact upon the best alloy temp. IMHO, not everyone agrees with that.

P.S. Added later: I forgot to mention, the hotter moulds will drop bullets that are more round too. It has to do with how each half of the mould expands, independantly of each other. Another IMHO goes here.

[captaint]

Your alloy matters also. Alloys higher in tin and especially antimony will generally cast larger boolits. No fight here...enjoy Mike

[williamwaco]

In my experience there the relationship between temperature and bullet diameter is not clear.

See :

http://www.reloadingtips.com/pages/exp_Bullet-diameter-vs-temp.htm


For my experiment.

[357shooter]

I did many tests regarding mould temps and published the results at: http://357shooter.blogspot.com/2011/02/extensive-mould-mould-temperature-test.html

Hope it helps.

[44man]

Temps mean a lot. The best size is where the boolit casts perfect, cold can also change things. But too hot will make the cavities expand to the outer edge of the blocks. It is 1/2 a hole at the edge, not a hole in the center of one.
A hole will have metal expand away from it and make it larger so you have to think different with half a hole at the edge. The edges can expand away at the parting line but the center will expand out. The boolit can measure larger at the parting line but smaller from the center. Out of round.
Many times I get a cherry too small and cast too small a boolit and the only way I can cut more metal is to get the mold hot, drop the cherry back in and turn it with a wrench. The amount of metal removed shows the cavity got smaller. I found boolits also get more round.
Have to work fast to keep the cherry from getting too hot, ruining the temper.
For an experiment I froze the blocks in the freezer. The cherry just wobbled and did not cut even if I warmed it. A cold mold has a larger cavity.
The misconception is when you close the mold you see a hole but what you have is two edges.