sizing when still warm vs. after bullets have cooled = difference in diameter?

Just got through casting, powder coating, and sizing 45 lb into 200 gr .45 RNFP

got to thinking (a lot of time for thinking when sizing 45 lbs of bullets): is the final diameter different depending if you size when bullets are warm vs. completely cooled?

My thinking is the warm ones will be sized to .451 and then drop down (contract) a few thousandths once cool while . . .

the already cooled ones will remain at .451.

I find the freshly PC ones size more easily than the fully cooled ones (not a biggie either way--just an observation) + I can size them while waiting for the next batch to bake

both shoot well with no differences I can see

Just curious . . .

I can't see where it would make any difference. The temperature differences involved are minuscule in regards to the alloy's coefficient of thermal expansion. There are changes in grain structure over extended periods of time, (many months, or even a year or more), but I'm not sure that even this would make a appreciable change in bullet dimension. A simple experiment should answer the question once and for all: Size half a dozen bullets while still hot to the touch and measure their diameter. Then set aside six other bullets and let them cool to room temperature. Size these cooled bullets and then measure them. I suspect that all the bullets will be the same, but taking the measurements will give the final word.

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Originally Posted by Walter Laich

Just got through casting, powder coating, and sizing 45 lb into 200 gr .45 RNFP

got to thinking (a lot of time for thinking when sizing 45 lbs of bullets): is the final diameter different depending if you size when bullets are warm vs. completely cooled?

My thinking is the warm ones will be sized to .451 and then drop down (contract) a few thousandths once cool while . . .

the already cooled ones will remain at .451.

I find the freshly PC ones size more easily than the fully cooled ones (not a biggie either way--just an observation) + I can size them while waiting for the next batch to bake

both shoot well with no differences I can see

Just curious . . .

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This is where I would do my own experimentation with my alloy, casting technique etc., etc., etc..
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Thanks.

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Originally Posted by Walter Laich

Just got through casting, powder coating, and sizing 45 lb into 200 gr .45 RNFP

got to thinking (a lot of time for thinking when sizing 45 lbs of bullets): is the final diameter different depending if you size when bullets are warm vs. completely cooled?

My thinking is the warm ones will be sized to .451 and then drop down (contract) a few thousandths once cool while . . .

the already cooled ones will remain at .451.

I find the freshly PC ones size more easily than the fully cooled ones (not a biggie either way--just an observation) + I can size them while waiting for the next batch to bake

both shoot well with no differences I can see

Just curious . . .

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The only way you'll know for sure is to check them with a micrometer. Not a caliper, a micrometer. That way you're checking your mold, your alloy and your process. If you can't detect any difference with a micrometer then obviously there's nothing to worry about.

Having said that, if they've cooled enough to handle without gloves I'll be very surprised if there's a measurable difference.

I try to size mine within a week or two, and let it go at that.
I'm sure the commercial casting places don't wait much longer than it takes for them to cool off.
But the difference should be somewhere in the category of splitting hairs.

I would think the difference in the diameter of your fingers as the blisters swelled would be far more relevant. The coefficient of linear expansion in pure lead is 29 Millionths of an inch per inch per degree Fahrenheit.

assuming ambient temperature of 70 °F and a fresh out of the oven 400 °F temperature and a bullet diameter of .452, we subtract t1 from t2 getting 330, multiply that times .000029, times .452 and end up with a theoretical maximum of ~.004 thermal shrinkage for a pure lead boolit. However, both tin and antimony will have the effect of decreasing this, as will the likelihood that you will not be picking up a 400 degree boolit but that it will be much cooler. I would expect any practical difference to be measured in ten thousandths of an inch, and would probably be undetectable without very skilled hands operating a very precise micrometer. Further, the resulting difference in diameter when both boolits reach equivalent temperatures would be measured in 100,000ths or less of an inch.

Hmmm. I'm guilty of sizing soon before I load my cast boolits. Normally I'll cast and rough inspect then store my boolits. When I have decided on a load, I'll lube and size, often the day before loading. I was digging around my shop and "found" a large plastic jar of Ranch Dog .432", 265 gr. RNFP with gas checks. My guess is they are 8 or 9 years old. If I dug deeper I would find the coffee can full of Lee 240 gr SWC I cast in 2009. I haven't tested old cast vs new cast, but have not noticed any difference so far. Sometimes I just cast to cast and store for a later need...

thanks for replies

I plan to do my own testing but in between lead shipments right now

something also I need to consider--using the same (and only one) cavity when casting some for the comparison--the cavities could be off a bit, too

my main reason for posting was to see if anyone had done this so I wouldn't be reinventing the wheel seeing as it's a mite warm in The Republic these days and the next cowboy match is over a week off

If you have a hardening alloy and you size them soon after casting, they will still grow to their final size. Had a friend that sized and loaded 45 Colts. Shot some right away, then put the gun away for quite a while. Went to shoot it again and cartridges wouldn't even fit the chamber because the bullet had grown so much.

I cast bullets and put them away. I size them when I'm going to use them. I've also done it the other way, sized them few days after casting and then put them away. The take away to sizing them right before you use them is you've destroyed some of the hardening, if it is an alloy that does hardend. Then others say when you shoot them the bore sizes them down and takes away the hardening. Hmmmm I haven't found that to be true as I've dug up thousands of bullets and they were pretty dang hard yet.

None of this pertains to pure lead bullets.

I belong in the cast and store them camp. I normally size and lube just before loading, because I primarily use FWFL and I don't want lube sticking together.

If I waterdropped for a very hard BHN, then I would size them as soon after casting as I could.

RObert

Some say jacketed bullets will cold weld to the case and cause accuracy issues if loaded too far in advance.

Lot's of things to worry about if one is so inclined.

I checked it and there is no difference in size from sized when warm and later cool. After a few weeks, depending on antimony content, they do grow 1-2 ten thousandths and a little more after a month or 2.

I powder coat then let cool to around 92, then size. Mine seem to hold.

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Originally Posted by Hannibal

Some say jacketed bullets will cold weld to the case and cause accuracy issues if loaded too far in advance.

Lot's of things to worry about if one is so inclined.

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There's a process called "galvanic corrosion" (my terminology may be off) where two different metals when in contact can "corrode" and stick together. Maybe if bullet jacket alloy and case alloy are different enough and when the conditions are just right they could "cold weld" together...

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Originally Posted by Hannibal

Some say jacketed bullets will cold weld to the case and cause accuracy issues if loaded too far in advance.

Lot's of things to worry about if one is so inclined.

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They used to. I think that was back in the cupronickel days with rounds that had been in storage for a while.

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Originally Posted by mdi

There's a process called "galvanic corrosion" (my terminology may be off) where two different metals when in contact can "corrode" and stick together. Maybe if bullet jacket alloy and case alloy are different enough and when the conditions are just right they could "cold weld" together...

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You have to have two dissimilar metals and their has to be an electrolyte. I most cases the electrolyte is water. So I would think if your ammo was wet or in water or high humidity that it would do it. Metallurgy isn't my field so I don't know.