How much does lead casting temp effect bullet size?

[hotwheelz]

So I generally run 650-700dg for normal casting but I got a new hollow point mold from Miha 45 200gr and was told to run hotter to get good fill out so I did 800dg and the mold works great these are water dropped so I dont have to wait to long to drop them from the mold I am not having any size issues with mold. So now I break out my other new mold from NEI and it 450-500-550-600gr 500mag. mold and ran it at 800 for the first 2 session but the bullets are droping on the small side .499-.500 these are also water dropped. I also ran some 115gr .30 cal boolits while i had the pot running still at 800dg and they seem to be droping small .308 insted of the .310 im used to getting out of this boolit. Probably gonna do some more casting this coming weekend but does lead temp really affect final boolits size? Or is it the water dropped that makeing them run small?

[williamwaco]

Interesting you should ask.

In response to another thread I tested this just last week.

Question:
How much does lead casting temp effect bullet size?

Answer:
Absolutely none.

I cast six bullets from the same cavity of the same mold from the same pot of alloy as it warmed up. Alloy was 50% range scrap 50% Linotype.

I cast at 500, 550, 600, 650, 700, 750, 800, 850.

Results are:

Average of 6.
500 .3585
550 .3585
600 .3586
650 .3590
700 .3588
750 .3585
800 .3589
850 .3590

Largest .3594 occurred at 700
Smallest .3585 occurred at: 500, 550, 750, 800

[runfiverun]

mold temp will affect boolit size, especially when it is combined with alloy temp.
alloy viscosity,and metals thing about expanding outward does have an affect.

[44man]

Mold temps change it, not lead temps. Hotter molds expand more and that makes cavities SMALLER.
Casting speed can affect size more then where you set the pot.
As you start with shiny to frosted, size will change.

[williamwaco]

Here are the complete results:


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

.

[Iron Mike Golf]

Mold temps change it, not lead temps. Hotter molds expand more and that makes cavities SMALLER...

I have to disagree with you on this one. Thermal expansion affects all dimensions. The cavity gets bigger as the mold block expands.

Read the example of a donut shaped item here: http://physics.bu.edu/~duffy/py105/Temperature.html

Alloy temp does not directly affect boolit size. It indirectly affects booilt size by transferring heat to the mold. Ideally, the amount of heat transferred from the alloy to the mold block offsets the heat lost between pours.

[williamwaco]

I have to disagree with you on this one. Thermal expansion affects all dimensions. The cavity gets bigger as the mold block expands.

Read the example of a donut shaped item here: http://physics.bu.edu/~duffy/py105/Temperature.html

Alloy temp does not directly affect boolit size. It indirectly affects booilt size by transferring heat to the mold. Ideally, the amount of heat transferred from the alloy to the mold block offsets the heat lost between pours.



Mike is correct !

.

[44man]

I have to disagree with you on this one. Thermal expansion affects all dimensions. The cavity gets bigger as the mold block expands.

Read the example of a donut shaped item here: http://physics.bu.edu/~duffy/py105/Temperature.html (http://physics.bu.edu/%7Eduffy/py105/Temperature.html)

Alloy temp does not directly affect boolit size. It indirectly affects booilt size by transferring heat to the mold. Ideally, the amount of heat transferred from the alloy to the mold block offsets the heat lost between pours.
Not so on a mold with half the cavity on the side. It expands OUTWARD just like all sides.
It is not the same as a hole in a block where meat expands away from it.
I make my own molds and once in a while the cherry is too small and so is my boolit. I get the mold real hot, drop in the cherry and I can remove a heck of a lot of metal.
Why do you think a fully frosted boolit is smaller?
So, my friend, we do NOT have a donut, we have one cut in half.

[runfiverun]

i hate this discussion.
but i do get bigger boolits from running things as cold as i can when casting.
but i mainly use steel molds.

[geargnasher]

44Man is correct here. I've measured mould cavities and they get both shorter and smaller as the block temperature increases.

That being said, for some reason I get small boolits most of the time when the mould is cool enough to cast boolits in the shiny/wrinkled stage, then they get to the optimum size at casting temp, and above the ideal mould temperature they begin to shrink.

Alloy temp has little effect on boolit size.

Gear

[txbirdman]

I had an experience just yesterday that proved to me that mould heat increases bullet size. I was casting with the Lee .312 185 gr. mould that I had lapped to throw a .302 nose which is the size needed for my Savage '06. After casting a few bullets I tried sticking the bullet nose first down the muzzle of the rifle. All were a perfect fit for awhile and then I noticed that the nose of the bullet was becoming too large. I started casting at 750 degrees so I slowly decreased the pot temp all the way down to 600 degrees. I still got large nosed bullets until I slowed down the casting cycle. If I would open the blocks and let them cool for several seconds then it would once again throw a .302 nose. However when I cycled a little too quickly the large nosed bullets were the results. From this experience I tend to agree with what Mike said. I don't think the casting temp has a direct effect on bullet size but I sure believe the temperature of the mould does.

[Larry Gibson]

mold temp will affect boolit size, especially when it is combined with alloy temp.
alloy viscosity,and metals thing about expanding outward does have an affect.

From 44man; "Mold temps change it, not lead temps. Hotter molds expand more and that makes cavities SMALLER.
Casting speed can affect size more then where you set the pot. As you start with shiny to frosted, size will change."

+1 on both.

The viscosity of the alloy is probably the real determining factor. Use a good alloy and there is little change as willianwaco's test shows. Use a poor alloy such as many batches of COWWs these days and results can indeed vary because of all the above mentioned reasons.

Larry Gibson

[44man]

44Man is correct here. I've measured mould cavities and they get both shorter and smaller as the block temperature increases.

That being said, for some reason I get small boolits most of the time when the mould is cool enough to cast boolits in the shiny/wrinkled stage, then they get to the optimum size at casting temp, and above the ideal mould temperature they begin to shrink.

Alloy temp has little effect on boolit size.

Gear
Yeah wrinkled is not right either But it is mold heat, too hot and boolits will be smaller. To hold just right is the answer. Cavities get smaller with too much heat.
Four seconds to cut a sprue! NUT"S, cutting molten lead. Cut molten lead with a glove to speed casting, another nut thing. Smear lead all over the top of the mold and under the plate. OH Hell, just Bullplate will solve it. Are you nuts?

[popper]

A hole in most metals gets LARGER with temp. A hole in a mould does funny things with increased temp. mostly due to clamping pressure. Yes they get shorter, out of round, etc. Pour temp only affects fillout. Figure out what yours likes and repeat, repeat - you get consistency. Write down what works. Alloy will make a difference if pours are consistent.

[44man]

Cavities are NOT a hole in metal. The hole is split in half and on the edge of the metal. You might THINK holding the blocks tight will change that but you will be wrong.

[detox]

I get more consistant diameters using a ladle vs. bottom pour, maybe consistant technigue and fill pressure has a little to do with it.

I have allways heard that higher casting temps (frosted bullets) will cause reduced diameters. I do not know for sure? Seems that my frosted bullets had very slightly smaller diameter?

[44man]

Notice a boolit will be more out of round when cast too hot. The boolit at the parting line will be larger due to the way the block expands.

[Cadillo]

Several variables at play here. Mould temp, melt temp, and alloy. They all affect the final outcome to some degree.

The hotter your melt, the less actual mass of material will fit into a given cavity, due to greater heat expansion, thus the lighter bullet will generally be smaller than one that was cast at a lower temperature.

I love my Lyman moulds, but they drop very small bullets unless I feed them an alloy that will effect the desired results. Adding enough monotype (high in tin and higher in antimony), allows me to greatly reduce my melt and mould temps while getting nice fill out and sharp edges. Lowered melt temp means more mass in any given cavity, and thus less shrinkage upon cooling. Additionally an alloy high in antimony tends to shrink less than one with less.

My rule of thumb with my Lyman's is that if I get any frosting at all, the bullets are right at the edge of being too small in diameter. Proper alloy and temp will prevent the frosting and keep diameters up to size. As long as my bullets fall bright and shiny, they are of adequate diameter.

I have several Mihec brass moulds, and they are a whole different animal. They have to be run a lot hotter or they just won't fill out properly. Fortunately their cavities are sized such that even when everything is hot, they still drop proper diameter bullets.