Pot temp variation and bullet weights,dimensions

[joeb33050]

I've been working on this on the CBA forum, my son set me straight, I think. Here's where I am now.
(Young) Joe is right: Pete Mink (and I) are wrong. As the temperature of the lead/pot goes up, bullets become smaller and lighter.
The coefficient of thermal expansion, (COE), in parts per million per degree C, at 20 degrees C, of Lead is 29, Aluminum is 23, Brass is 19 and Iron/Steel is 11.1.
As the temperature of these metals increases their volume increases and specific gravity or density decreases.
At normal casting temperatures, lead and lead/tin/antimony alloys are molten.
Assume that the mold temperature is determined by the alloy temperature without outside heating. Then mold temperature is less than alloy temperature, cycling as alloy is poured, hardens, solidifies, and the casting is removed from the mold.
Since lead (and its alloys) has a higher COE than any of the three common mold metals, it shrinks more on cooling than any of the mold metals. Then for any increase in pot temperature, the resulting castings will be both smaller in all dimensions and lighter than if cast at a lower pot temperature.
How much smaller/lighter?
It is clear that the COE is not linear, since COE is specified at a temperature. We don't know the COEs at ~650-850 degrees F.
I don't know if the COE for lead/tin/antimony alloys is ~29 in the ~650-850 F region.
However: Fiddling with the numbers after making some probably unwarranted assumptions suggests that a 10 degree F change in pot temperature might cause a reduction in bullet weight of a tenth of a grain in a 200 grain bullet.
As the pot gets hotter, the bullets get smaller and lighter.
joe brennan

[9.3X62AL]

Interesting concept, Joe. My observations to date are consistent with your theory to some degree, at least. With larger-caliber boolits (.35"+) I have gained from .0003" to almost .001" (mean measurement) by running 92/6/2 at 675* as opposed to 800*. I tracked this pretty closely a couple years ago, and had not considered your theory as to cause--the positive effects were enough for me. I lowered casting temps across the board with all molds. Reject rate diminished markedly, too.

[44man]

I find my best boolits are when the pot and mold are close in temp. When clean, sharp boolits come out without wrinkles, it is just right. If I heat the lead a little and the mold evens out, I can get a larger boolit but if anything gets too hot, the size and weight goes down. The very worst is a mold hotter then the lead, that will give a small boolit. I make that mistake if the boolits are wrinkled and I heat the mold more. The first several boolits will be small and frosted but as soon as things get evened out, the next boolit will be OK even though still frosted a little.
If I am making soft boolits and am casting at 750 degrees, going to 800 will give me a larger boolit but too hot has the reverse effect. I never figured out if it is the alloy or what Joeb says.
Since none of us uses the same alloy or even the same mold material, everyone can find something different.
Rapine told me if I want a little more size to my soft BPCR boolits, raise the temp a little so the mold expands more. Mold metal will only expand so far and quit growing so my guess is there is a small window there. I can't hold the temp close enough to worry about it.
It would be interesting to have a graph showing every change at all temperatures for a mold and alloy but I don't see any practical use. I just wonder if there is a swing towards larger as temp rises and then a swing back the other way.
Something I never gave much thought to and just try to cast at the point boolits are perfect. I do know that with my alloy if I get anything too hot, the boolits will not fill out and the GG's will start to round off. Too cold and bases don't fill and too hot, the rest of the boolit suffers. The mold I last used HAD to be 800 degrees while others can make great boolits at much lower temps.

[9.3X62AL]

Agreed, 44--some molds have "personalities" and temp preferences. There is considerable science to this hobby, but a big part of it remains "art". Art may just be the cumulative effects of variables we choose to not cancel out of the equation, too.

If I can venture a guess here.....OP Joe Brennan is engaged in chasing down the uncancelled variables to the greatest degree possible. More science/less art, in other words. This theme runs through a lot of his threads and posts, and is a commendable pursuit. My degree of sophistication and patience for detail is not at Joe's level, but I can surely appreciate his efforts--and hope in my own small way to lend my experiences and observations to his pursuit.

[44man]

I agree, I am so old that if I need something from a math book, I stare at it in bewilderment. I have to read what others do but most of the time I am like this :confused: when it is over my head. I can't explain all the stuff that happens and as soon as I form an opinion, I find that it doesn't work all the time.
I refuse to think anymore, rather get a drink. :drinks:

[leftiye]

Another factor that possibly furthers this effect of lighter boolits with higher temperatures is what we've been discussing in regards to frosting on other threads. I recognize that some alloys might cast hot, and still not frost, but the most common alloys for smokeless almost universally will frost if hot enough. So, in addition to (not disputing joe's idea) the lead shrinking faster than the mold does; the formation of crystals on the surface of boolits that don't freeze instantly with the concurrent migration of other factor alloys that freeze more slowly away from the surface of the boolits contributes to lighter boolits, as the mold isn't as completely filled in these cases. Problematically, these antimony bearing alloys don't shrink as much as the purer lead, or lead tin alloys do.

Another factor here is the expansion of the mold at higher temperatures. The cavity actually gets larger as the whole mold block expands (the cavity doesn't shrink). It was a long time ago that I measured this, and I might be mistaken, but that's how it looked to me (and measured). So, we have to trade off the mold expanding against the boolit shrinking. The mold doesn't cool much during the casting cycle - not say a hundred degrees between boolits anyway. Plus it is the mold temp when the alloy is inserted that matters- ie. the cool point in the casting cycle. So mold temp only determines final mold size, and cooling rate of the alloy, the shrinkage of the lead stands alone and doesn't relate to the expansion of the metal in the mold except as noted in making the cavities larger and impacting the cooling rate of the lead. I'm not saying that hotter alloys don't produce lighter boolits. I'm saying that the mold expanding interferes with this being a calculable (at least not easily) quantity. At least not linearly calculable. The best that can be said is it's a very confusing situation as to what leads to the final outcome.

[fourarmed]

I just did a quick calculation, assuming the COE is effectively constant. I assumed pure lead in an iron mold, nominal diameter 0.452", one cooling from 850 F to room temp, the other cooling from 650 F to RT. The difference in diameter due purely to thermal contraction is about 0.0009". If you neglect the expansion of the mold from 650 to 850, the difference is more like 0.0015", so the expansion of the mold is definitely a factor. The difference would be proportionately smaller for smaller diameter boolits. So the numbers are in good agreement with the values that Al observed. I love it when that happens.

[454PB]

The other day I was casting with my RCBS .430-250, and decided to compare the mould temperature to the pot temperature with my IR thermometer. It was exactly half......alloy was 720 degrees, mould was 360 degrees immediately after dumping the boolits.

Just something of interest to think about.

[joeb33050]

The other day I was casting with my RCBS .430-250, and decided to compare the mould temperature to the pot temperature with my IR thermometer. It was exactly half......alloy was 720 degrees, mould was 360 degrees immediately after dumping the boolits.

Just something of interest to think about.

I find that hard to believe. Would you take a lot of additional readings and share them with us?
All my molds, from small 45 caliber blocks to large 22 caliber blocks, want to be hot or bullets have wrinkles and or defects. I get the mold hot by putting it on the edge of the pot, and sometimes in the alloy. Either way I suspect that the mold blocks are close to the temperature of the alloy when casting-at the time I'm pouring the alloy in the mold.
When the alloy goes from a liquid to a solid, that's a phase change and there's a release of a lot of heat. Somehow, from pouring to opening the mold, a LOT of heat has to go away; I always thought mostly by conduction into the air. (I'm having good luck cooling the mold for faster casting by putting the mold bottom on an upside-down muffin tin---the water in the casting area bothers me.)
If you are right, then maybe the mold is able to get rid of a LOT of heat very quickly. And if that's true, I have to re-think what's going on.
If your readings are a true picture, it reinforces the notion that large blocks with a lot of surface area make it hard to cast good bullets.
So, please take a lot of readings as you cast in a manner to get good bullets, this may be of some importance.
Thanks;
joe brennan

[joeb33050]

Another factor that possibly furthers this effect of lighter boolits with higher temperatures is what we've been discussing in regards to frosting on other threads. I recognize that some alloys might cast hot, and still not frost, but the most common alloys for smokeless almost universally will frost if hot enough. So, in addition to (not disputing joe's idea) the lead shrinking faster than the mold does; the formation of crystals on the surface of boolits that don't freeze instantly with the concurrent migration of other factor alloys that freeze more slowly away from the surface of the boolits contributes to lighter boolits, as the mold isn't as completely filled in these cases. Problematically, these antimony bearing alloys don't shrink as much as the purer lead, or lead tin alloys do.

Another factor here is the expansion of the mold at higher temperatures. The cavity actually gets larger as the whole mold block expands (the cavity doesn't shrink). It was a long time ago that I measured this, and I might be mistaken, but that's how it looked to me (and measured). So, we have to trade off the mold expanding against the boolit shrinking. The mold doesn't cool much during the casting cycle - not say a hundred degrees between boolits anyway. Plus it is the mold temp when the alloy is inserted that matters- ie. the cool point in the casting cycle. So mold temp only determines final mold size, and cooling rate of the alloy, the shrinkage of the lead stands alone and doesn't relate to the expansion of the metal in the mold except as noted in making the cavities larger and impacting the cooling rate of the lead. I'm not saying that hotter alloys don't produce lighter boolits. I'm saying that the mold expanding interferes with this being a calculable (at least not easily) quantity. At least not linearly calculable. The best that can be said is it's a very confusing situation as to what leads to the final outcome.

I understand the first part, about frosting.
I don't understand the second part.
We heat the alloy and the mold from room temperature. Both get larger, but the alloy expands more than the mold.
We cast a bullet that now shrinks more than the mold shrinks as they cool down-both to room temperature.
At room temperature the mold cavity is smaller than it was when hot; and the bullet is smaller than the room-temperature mold cavity, because it shrinks more than the mold.

Are you saying that something else is going on? If so, please explain, I've got this tiger by the tail and can't let it go until I understand it.
Thanks;
joe brennan

[44man]

Joeb, I just got out one of my BPCR boolits and the mold. I cast these hot some time ago with a 30 to 1 mix. I set the boolit in the mold and gave it a little push and put the other block on. There is a 3/64" gap between the blocks and I would have to use a vise to close the mold. I removed one block and could not get the boolit back out of the other half even though it was not all the way in. I had to use a knife and ruin the boolit to remove it.
My boolit is a LOT larger then the cold mold! I can't tell how much because all I have is a vernier that won't measure the cavity right.

[leftiye]

Joe,
The expansion and shrinkage of the alloy proceeds as a separate phenomenon from the mold's expansion and shrinkage. The mold only serves to identify the starting size, and to influence the cooling rate. It's not about interaction between the amount of expansion/over temperature between the two metals. The mold is at approximately the same temp at each time that it is filled and heats up as the lead cools.

Whereas the mold does expand volume wise, it is nevertheless in solid phase throughout the process, and dimensional expansion of the blocks (while being heated up only) results in larger cavities which counteracts the cooling/shrinkage of the alloy as it goes through its phase change. This exansion of the blocks probably pretty much stops when operating temp is reached.

I'm pretty sure that we should accept 454Pb's thermometer readings. Yes the sample is very small. But unless it was faulty, it is probably within the statistical norm and further readings will validate it. One thing that would be nice to know that would be gained by further readings (with this and other molds) would be to see how wide the range of mold temps is at ideal mold temps. Unless you have one of these IR thermometers one has no way of actually knowing the temp of the moldwhich is being cast with. I've heard (FWIW) a temp of 400 degrees previously. Perhaps the fact that the mold isn't heated as hot as the alloy has a bearing?

I'd guess that the ability to absorb heat (at whatever the mold metal's rate is) at a set rate probably will result in there being a single ideal mold temp (narrow range) for a given alloy. This also would be good to know. Ideal mold temp would vary for casting alloy, and also for mold parent metal (rate of heat absorbtion).

44man, Don't suppose the mold shrank when it cooled? In this cae more than the boolit apparently.

[Firebird]

After several tries I am still having problems trying to explain my point here, so bear with me.
Since the liquid lead alloy is always going to solidify at the same temperature, taking the exact shape of the mold (hopefully with full fill-out etc) at that temperature, why should the starting temperature of the liquid alloy even matter? I can see why the temperature of the mold could make a slight difference, and a mold would run hotter if the liquid lead alloy temperature is higher; but wouldn't that make the bullets bigger, not smaller at a higher liquid lead alloy temperature?

[44man]

Leftiye, that is correct, I was only countering what Joeb said about the boolit being smaller then the room temperature mold. Not so depending on the expansion point of the mold when casting. If my boolits would have been cast at a lower temp and cooler mold, they might have fit back in but I never seen a boolit smaller then the cavity. When the lead cools in the hot mold, it shrinks enough to come out but remember the mold is still expanded from heat. When the mold cools and shrinks, the cold boolit will either be the same size or larger then the cavity depending on the casting temp.
I have lapped too many molds of all sizes and it is very hard to get a boolit back in the mold. The addition of a little abrasive will never allow the blocks to close until the boolit is worn down. Thats why a lapped mold never stays round because of the lead force on the block edges. Even a cherry will cut larger at the block edges because of the lead factor as the cutters touch the edges. Ever notice when you size a boolit from a cherry cut mold, the boolit sizes more on one side of the parting line?
If I get a mold too small from a cherry too small, I freeze the blocks and heat the cherry a little. Then cut by hand to enlarge the cavity. I get a lot of metal out of the mold.
I think (But take it with a grain of salt.) as you go from a cooler casting session to a hotter one, the boolits will increase in size but once the mold reaches maximum expansion and you keep making the lead hotter, the lead expands more from the heat and can shrink more when cooling resulting in a smaller boolit. They still will not go back in a cold mold easy because you will be back to the size from a cooler mold and pot.
So if you want a larger boolit, cast at the maximum expansion point of the mold and no more. If you want a smaller boolit, cast at the point the boolit just gives a good fill out. Now we need to know what the mold and lead temperature is for each mold and size boolit. Is it too much work and figuring? I think so, do what works and don't dwell on it.

[leftiye]

Firebird has an interesting point. It may not be too important what temp the alloy is at as it freezes at the same temp regardless. However if it heats the mold more because it is hotter, then this affects as cast diameter. And this probably isn't all the story because we all have gotten varying size boolits with one mold/alloy combination. I suspect that with hotter alloys the surface freezes and then is pulled inward by the rest of the boolit as that freezes. Nuff fun yet?

[454PB]

Joe, I'll do a little more temperature testing the next time I cast.

Here's another interesting point:
My loading/casting room is heated by an electric heater in cold weather. This is not your typical 1500 watt milkhouse heater, it's a 240 volt 3000 watt floor heater. I use it to preheat my moulds while I'm melting a pot of alloy by laying the mould on the top of the heater. I use the IR gun to see when the mould is ready to start casting. At around 250 degrees, the first pour is acceptable and still shiny, and the second is fully filled out.

I encourage others that have an infrared thermometer to do some testing. The results might surprise you. A bullet mould is a radiator, and disperses heat rather quickly, especially when it's empty.

[powderburnerr]

to add to 454pb statement

I have a couple adjustable base nose pour moulds and one has a small adjusting bolt , it requires around 480 to cast a bullet and a 30 sec cycle to get good bases , if using the other mould with a heavy adjusting bolt I have to slow to 1 a minute to keep the mould cool enough to make a good bullet with out slumping . I think that the mould is a good radiator and the base pins act as a heat sink drawing heat out of the mould , the thinner wicking heat faster than the heavier, both of these moulds are close to 600 gns, .....Dean

[joeb33050]

I'm still digesting what's written above. The fact that the alloy silidifies at a temperature, regardless of pot temperature, is of great interest.
I took some molds, stored with bullets and sprues in the cavities/sprue hole, opened them, took out the bullets and put the bullet/s back.
Borton Darr 308 165, bullet was sticky coming out, back in fine.
Lyman 429421 DC both fell out, both went back in fine.
Lyman 308403 had to knock handle hinge to get it out, it went in fine.
Hoch 317165 bullet fell out, easy to put it back in.
In all cases I had to put the bullets back in the way they were cast, but they all went in and the molds closed tight.
Most alloys soft, 25:1 or so.
joe brennan

[Dye]

Joe, I'll do a little more temperature testing the next time I cast.

Here's another interesting point:
My loading/casting room is heated by an electric heater in cold weather. This is not your typical 1500 watt milkhouse heater, it's a 240 volt 3000 watt floor heater. I use it to preheat my moulds while I'm melting a pot of alloy by laying the mould on the top of the heater. I use the IR gun to see when the mould is ready to start casting. At around 250 degrees, the first pour is acceptable and still shiny, and the second is fully filled out.

I encourage others that have an infrared thermometer to do some testing. The results might surprise you. A bullet mould is a radiator, and disperses heat rather quickly, especially when it's empty.

454PB
The next time you cast will you try this.
1 Have you alloy temperature about 125 degrees above slush stage of the
alloy (125 - 150) degrees about the norm.
2 Have the cavity of the mould about 325 degrees. (Maintain that bye
the casting rate ) Looks like 300 -350 is the cavity temp range on a 1 or
2 cavity mould
3 Cut the sprue with a gloved hand and pay attention to the base of the
bullet for square clean cut. The ambient temp. will change the above a little
but the casting rate should be able to maintain these temps.

Be carefull Dye

[454PB]

I use the "frosty boolit" method for WW alloy. After casting for over 35 years, I have learned that the best results for me are to cast at a temperature that produces a very light frosting. I usually pitch the first few shiny boolits back into the pot, the keepers start when I see some frosting. I didn't even own a casting thermometer until a few months ago, and all it has done is confirm what I already knew.

Your 300 to 350 degree mould temperature agrees with what I said in my original reply to this thread. I use both aluminum and steel moulds, and they both require about the same pot temperature, the only difference is that the aluminum ones need to be cooled about every third cycle by touching the mould base on a wet cloth. I usually cast with two moulds to speed things up and avoid the cooling technique.

[trk]

After several tries I am still having problems trying to explain my point here, so bear with me.
Since the liquid lead alloy is always going to solidify at the same temperature, taking the exact shape of the mold (hopefully with full fill-out etc) at that temperature, why should the starting temperature of the liquid alloy even matter? I can see why the temperature of the mold could make a slight difference, and a mold would run hotter if the liquid lead alloy temperature is higher; but wouldn't that make the bullets bigger, not smaller at a higher liquid lead alloy temperature?

If the mould temperature is say "A" and the alloy temperature "A + 200 dF" then the alloy will be heating the mould a certain amount. The resulting temperature of the mould at the time of solidification of the bullet will be "C" (somewhere between). Hence, my conclusion, that both temperatures are influential (because the higher the temperature of the mould, the smaller the diameter of the cavity).

The diameter of the hole is dependant on the temperature of the mould.

Note the H.S. physics experiment of measuring a hole in a disk and the steel ball passes through it unless the disk has been heated - making the hole smaller. When the disk cools after being heated, the ball drops through.

(Note also if the disk is a LARGE ring it acts differently - like a ring-gear that is heated to expand it to place it around a flywheel. The proportional thickness of the wall is thin compared to the diameters of the hole and OD.)

I assume that the alloy shinks faster than either aluminum or iron, as waiting a few moments allows the bullets to drop out easily.

[leftiye]

Trk,
My take on the above is that the disk, and a mold cavity are not synonymous. Due to the fact of the two mold halves being distinct pieces from each other, each half expands separately and independently. In effect everything expands away from the centerline of the mold. Therefore everything grows in size including the cavities.

In your example of the disk the piece of metal expands away from the " pitch circle of the washer (somewhere about halfway between the outer edge of the disk, and the hole in the center). As the disk is bound together (one piece) what actually happens is that the inner part of the disk is compressed and the center hole gets smaller.

You can test this by cutting the disk in two, and measuring the diameter of the center hole before and after heating (use 350 degrees in your oven). The hole should get larger in this scenario.

[joeb33050]

Thanks to all for the help.
You've turned my thinking on it's head.
I thought I could find some info on the melting point of various tin antimony lead alloys, but I can't.
Here's where I am.
Starting from cold, these alloys go from hot to slushy to liquid. Starting from hot there's liquid, slushy, then hot and solid as the metal cools. There may be a temperature range where there is a liquid and slush present at the same time.
"Eutectic" alloys have the characteristic that there is no slushy stage, the metal goes from solid to liquid without the slushy stage, as heat increases.
I have two new notions to contend with. First, any given alloy turns solid at a certain temperature, without regard to the temperature of the pot, the metal in the pot, or the mold. Second is the idea that mold temperature while casting good bullets is as low as 250-360 degrees F.
Alloy temperature, in the pot, casting good bullets, is in the vicinity of 700-850 F; all depending on something or other. The alloy/pot temperature is adjusted by the caster to get the bullets filled out and good loooking, while minimizing the amount of time it takes for the sprue and bullet to harden so the base isn't torn or pitted.
Slushy or soft temperatures are in the 500 degree neighborhood, with hard being around 470 degrees; all if I understand the heat-treaters correctly.
Alloy at 700-850 degrees goes into the mold that is at 250-360 degrees. The mold gets hotter and the alloy gets colder, the whole megillah getting to some temperature-maybe 600 degrees, then cooling to about 450 degrees where the bullet is hard and can be removed from the mold without bending.
It seems clear that the mold has to be pretty cool when the alloy is poured in, because the mold has to get rid of the heat in the alloy and the heat released during the phase change from liquid to solid.
So, it seems that the mold is a very efficient heat disperser, able to get rid of a lot of heat and reduce its temperature a lot in the time from the release of the bullet to the time of the next fill.
Somewhere, hidden in this, is a change in bullet weight and dimensions; but that change has nothing to do with the pot temperature because, as Firebird points out, the solid temperature is independant of the pot temperature.
Are we almost there?
joe brennan

[trk]

Trk,
My take on the above is that the disk, and a mold cavity are not synonymous.
...



Good point. The metal has to go somewhere when it expands. Theory at this point. It could well be that the bullet cavity changes size differently in different dimensions. That would make the bullet more oval. ALL discernable by testing.

It IS time to get the drill and to embed the thermocouples!

[44man]

I have no way to measure mold temperatures but I put the mold in my little furnace on a hot plate. The thermometer says 500 degrees when I start casting and the first boolit will be perfect. If I remove the mold before it soaks in the furnace long enough, all boolits will be wrinkled until I either heat it with a torch or cast a bunch fast.
I have my doubts that a mold as cold as 250 to 360 degrees will make a boolit of any kind. I don't think the surface temperature of a mold will give the whole story. It might be better to measure the cavity as soon as a boolit is dropped.

[Firebird]

joeb33050 - Lymans "Cast Bullet Handbook" 3rd edition has an article Metallurgy of Molten Lead Alloys that contains phase diagrams for Lead/Tin, Lead/Antimony, Lead/Zinc and also one for Lead/Tin/Antimony that I haven't been able to really figure out.

[454PB]

There are melting temperatures for several common alloys here:

http://www.lasc.us/CastBulletNotes.htm

[Nueces]

Hi, Guys

May I please offer a clarification on the heated ring/disk situation? When I was a physics student, I also 'intuited' that the inside of the ring shrunk when heated. Once the science overrode my head, I found it much easier to picture (and calculate) what was happening.

Whenever a solid body is evenly heated, ALL linear dimensions change according to the coefficient of expansion. By linear dimension, I mean all dimensions measured in inches. In the case of a ring, both inner and outer diameters (and circumferences) are increased by the same fraction, ie (1 + e), where e = coefficient of thermal expansion and is assumed to be positive. The size of the ring matters not. There is no crossover size beyond which the inner surface contracts. If that were to be true, then there would have to be a critical size at which no thermal expansion took place - obviously not the case.

Picture a disk being slowly heated. It's diameter increases, right? Now, mentally remove the interior part of the disk so that a ring is left. The inside arc of the ring was the outside arc of the removed disk, BOTH of which have expanded from heating. Hope that's clear. A disk is just a ring with inside diameter zero, so, if the inside diameter shrinks, a heated disk would 'pooch' out at the center. That is not observed, either.

The old experiment involved heating the ring to allow the ball to pass through. If a cooled ring were to expand, then you've got a substance with a negative coefficient, pretty rare at room temperature.

Mark

[charger 1]

Lordy Lordy.and to think, I've just been pourin metal into a mold and a boolit pops out. I'm now startin to wonder if it indeed is a boolit or merely a cleverly disguised watchamacallit.... I dont think I'll ever look ay my pot the same way again

[w30wcf]

This topic has stirred my memory a bit. Anyone recall the name Merrill Martin? He wrote a number of interesting articles on cast bullets for Precision Shooting magazine way back in the 1980's.

Anyway, one article he wrote delt with making "match grade" cast bullets consistantly by monitoring both the pot and mold temperature. He installed a thermometer with a short stem directly into a .30 caliber NEI mold block.

He used an alloy of 50/50 w.w./lead and added 1% tin. That way he could heat treat the bullets to 20-25 brinnell and then draw them back down to whatever hardness he wanted.

He used a pot temp. of 800F and found that with that particular mold he was using, 340F was the ideal mold temperature when starting to pour the first cavity. Mold temp rose to 350F by the time the first cavity was filled and the second one about to start.

After degating and removing the bullets from the mold he held the mold over a fan (about 5 seconds) to get the temp back down to 340F. The process was then repeated.

The result of his process was 350 "match grade" bullets in 2 1/2 hours and most within 1/10 gr.

Prior to his casting session he coated his blocks with NEI mold prep, and touched up the vent lines using a 3 corner swiss file. He used kitty litter on top of the melt and drop poured using a Lyman 20 lb furnace with about 1" distance between the spout and the sprue plate.

He mentioned that different molds might make their best bullets at different temperatures so one needs to experiment. He mentioned that he has other molds that do their best @ 300F, 400F, 450F and 1 that needs to be 500F.

I'd say that he has it down to a science!:drinks:

w30wcf

[georgeld]

ahhhhh sheeet you guys!!

Keep the melt between 700 and 800 and keep casting steady, drop 'em in a bucket
when you dump the mold.

when you're ready, size 'em all thru the same die adn they'll be the same.

So what's it matter, left hand mold, or right hand??

[44man]

That was said the best! :drinks:

[joeb33050]

joeb33050 - Lymans "Cast Bullet Handbook" 3rd edition has an article Metallurgy of Molten Lead Alloys that contains phase diagrams for Lead/Tin, Lead/Antimony, Lead/Zinc and also one for Lead/Tin/Antimony that I haven't been able to really figure out.

Thank you, I found it and almost understand the lead/tin/antimony diagram.
Is there anyone out there who would scan this diagram and turn it into a .jpg drawing? If I had that I could blow it up and understand it better.
Thanks again;
joe brennan

[joeb33050]

Thanks to the Cast Boolits members who contributed to this topic and (I hope) got me thinking correctly. Especially 454PB, Firebird, 44man, 9.3X62AL, leftiye,W30WCF et al.
Every lead tin antimony alloy has a freezing point. A chart showing the temperatures where the alloy starts to become solid may be found in the Lyman Cast Bullet Handbook, Third Edition, page 47.
All alloys other than eutectic alloys, such as linotype, have a slushy stage before the casting is hard. Here are some starting-to-become-solid temperatures from the chart mentioned above:
WW .5% tin, 4% antimony 560- F
Lyman #2 5% tin, 5% antimony 540+ F
Linotype 4% tin, 12% antimony 464 F Eutectic, ~480 F nearby
Mold temperatures in the 250-350F range just prior to the pour have been measured and mentioned several times. I was, and still am, surprised that mold temperatures are this low. But while surprised, I have learned.
No matter what the temperature of the mold and alloy as the pour is made, the mold and alloy must be at the freezing temperature when the alloy begins to freeze. For example, with Lyman #2, the alloy might be at 800F in the pot, the mold might be at 350 F, as the pour is made the alloy in the mold cools as the mold heats up, after the mold is removed from the spout both the alloy/bullet and the mold cool.
Thus, if the mold and bullet are at the same temperature when the bullet freezes, the temperature of the pot of alloy has no effect on the weight or dimensions of the bullet. And, the room temperature bullet is always a smidgn smaller than the room temperature mold, the smidgn being the same for any alloy.
I think that this goes against my experience and that of others, but am beginning to suspect my memory. Perhaps an experiment is in order.
Some ask why I/We care about this stuff. I'll start another thread, "Molds and Heat" to approach the possible practical application of what we've learned.
If I'm wrong on the synthesis above, please let me know!
Thanks;
joe brennan

[leftiye]

Joe,
Not wrong. I do have a slightly different feel for the subject. I don't think that the melt, and the mold are at the same temp until well after the boolit solidifies. Maybe never, maybe somewhat before the boolit is dropped.

My perspective would be that the mold temp is probably almost a constant in the casting process. Constant for a given mold with the alloy in question that is. There is an ideal temp for each mold for each alloy. I'm not saying that the mold doesn't heat up and cool down during the casting cycle.

We have all probably had a mold so hot that the boolit remained molten, and poured out when the mold was opened. And we've all had frosted boolits. My feeling about frosted boolits is that frosting results when freezing (cooling) progresses at a slow rate that allows time for crystals to form on the surface of the boolit. The mold in this example being hot enough that the boolit freezes slowly. BUT for this and all cooler mold conditions the boolit does solidify, and therefore during the only point in time that really matters (while the boolit solidifies), the mold is cooler than the boolit.

So you come up with the situation being that the only interrelation between the mold and the melt is how fast the mold cools the boolit. This is what makes me think that the mold temp is relatively fixed (does vary some, also varies between molds), for the given mold with a given alloy. It might even be possible to predict mold and alloy temperatures for different boolit designs in molds made of different metals, with different alloys.

I wouldn't want to argue with you about final sizes of the boolit as compared to the mold. Actually seems to me not to matter. But with different alloys shrinkage varies, and Antimony bearing alloys shrink much less than pure lead boolits do, and they end up larger than the mold at room temp. Doesn't disprove your idea, just interferes with it. Also due to the mold being cooler than the freezing temp of the alloy at all times, there is a further problem with predicting the amounts of shrinkage.

[joeb33050]

Joe,
Not wrong. I do have a slightly different feel for the subject. I don't think that the melt, and the mold are at the same temp until well after the boolit solidifies. Maybe never, maybe somewhat before the boolit is dropped.

My perspective would be that the mold temp is probably almost a constant in the casting process. Constant for a given mold with the alloy in question that is. There is an ideal temp for each mold for each alloy. I'm not saying that the mold doesn't heat up and cool down during the casting cycle.

We have all probably had a mold so hot that the boolit remained molten, and poured out when the mold was opened. And we've all had frosted boolits. My feeling about frosted boolits is that frosting results when freezing (cooling) progresses at a slow rate that allows time for crystals to form on the surface of the boolit. The mold in this example being hot enough that the boolit freezes slowly. BUT for this and all cooler mold conditions the boolit does solidify, and therefore during the only point in time that really matters (while the boolit solidifies), the mold is cooler than the boolit.

So you come up with the situation being that the only interrelation between the mold and the melt is how fast the mold cools the boolit. This is what makes me think that the mold temp is relatively fixed (does vary some, also varies between molds), for the given mold with a given alloy. It might even be possible to predict mold and alloy temperatures for different boolit designs in molds made of different metals, with different alloys.

I wouldn't want to argue with you about final sizes of the boolit as compared to the mold. Actually seems to me not to matter. But with different alloys shrinkage varies, and Antimony bearing alloys shrink much less than pure lead boolits do, and they end up larger than the mold at room temp. Doesn't disprove your idea, just interferes with it. Also due to the mold being cooler than the freezing temp of the alloy at all times, there is a further problem with predicting the amounts of shrinkage.
"I don't think that the melt, and the mold are at the same temp until well after the boolit solidifies. Maybe never, maybe somewhat before the boolit is dropped."


I agree, see the chart I posted on the "Molds and Heat" thread.

I'm still surprised by the 250-350 degree mold temperature reports-that is what changed my thinking on this.
joe brennan

[fourarmed]

Keep in mind the basic rule: Heat flows from high temperature to low. (Everything flows downhill unless you do work on it.) So even if the inner surface of the mold is at or near the temp of the boolit, the outer surface will be cooler. Iron is a poorer conductor of heat than aluminum or brass, so in order to shed a certain amount of heat in a given time (and therefore remain at a roughly constant temp), the temperature gradient from inside to outside has to be larger for an iron mold than an aluminum one. So the iron mold has to be either hotter on the inner surface or cooler on the outer surface than an aluminum mold doing the same job.

What does this mean in the context of this thread? That is left as an exercise for the student.

[felix]

Not only that, Robert, but these so-called iron blocks are typically made out of cast iron which has usable air holes throughout the "steel". This insulation helps greatly in making 22 boolits at a slower, more user friendly, pace. ... felix

[montana_charlie]

these so-called iron blocks are typically made out of cast iron If true, I find that quite surprising...
CM

[joeb33050]

"Keep in mind the basic rule: Heat flows from high temperature to low. (Everything flows downhill unless you do work on it.) "

We knew that.

"So even if the inner surface of the mold is at or near the temp of the boolit, the outer surface will be cooler."

There will be differences in temperature from place to place on the mold and bullet, and these gradients and temperatures will change in time as the various operations are performed. And, keep in mind that the "inside" of the mold becomes the "outside" after the bullet drops.

"Iron is a poorer conductor of heat than aluminum or brass"

We knew that.

, so in order to shed a certain amount of heat in a given time (and therefore remain at a roughly constant temp), the temperature gradient from inside to outside has to be larger for an iron mold than an aluminum one. So the iron mold has to be either hotter on the inner surface or cooler on the outer surface than an aluminum mold doing the same job.

This may be true, but I don't know it to be true. There's a lot going on here, some of it has to do with the specific heat of the mold metal and the heat transfer rates of those metals. Black iron radiates better than shiny aluminum? Than shiny brass?
Keep in mind that an aluminum and an iron mold don't have to shed the same amount of heat in a given time.


What does this mean in the context of this thread? That is left as an exercise for the student.

I'm not a fast caster, and I average about 100 bullets per hour. This means that the entire cycle has to happen in less than .6 minutes or 36 seconds, counting the bad bullets. And in the mold-cooling time, the mold falls from ~500+ F to ~300F. A lot of heat is going away quick. Hence my surprise.
joe brennan

[joeb33050]

Not only that, Robert, but these so-called iron blocks are typically made out of cast iron which has usable air holes throughout the "steel". This insulation helps greatly in making 22 boolits at a slower, more user friendly, pace. ... felix

Lyman has printed that their blocks are made out of a semi cast iron semi steel called "meehanite". I suspect that this has more carbon than steels, less than cast iron. I've never read nor heard that any of the irons/steels had intentional or planned porosity = air holes, and just looked at three molds under a magnifier and don't see any holes. I can and may check the density of a mold half to see if there's any air holes. Where can I read about this, Felix?
joe brennan

[joeb33050]

I'd like to finish up on this original topic. Here's where I am. Anybody?

LEAD POT TEMPERATURE AND BULLET WEIGHT AND DIAMETER

(Thanks to the Cast Boolits members who contributed to this topic and (I hope) got me thinking correctly. Especially 454PB, Firebird, 44man, 9.3X62AL, leftiye,W30WCF et al.)
The original question was: Do variations in the temperature of the pot/alloy, as the thermostat cycles, vary the weight/dimensions of the cast bullet?
I now think not, and here's why:
Every lead tin antimony alloy has a freezing point. A chart showing the temperatures where the alloy starts to become solid may be found in the Lyman Cast Bullet Handbook, Third Edition, page 47.
All alloys other than eutectic alloys, such as linotype, have a slushy stage before the casting is hard. Here are some starting-to-become-solid temperatures from the chart mentioned above:
WW .5% tin, 4% antimony 560- F
Lyman #2 5% tin, 5% antimony 540+ F
Linotype 4% tin, 12% antimony 464 F Eutectic, ~480 F nearby
Mold temperatures in the 250-350F range just prior to the pour have been measured and mentioned several times. I was, and still am, surprised that mold temperatures are this low. But while surprised, I have learned.
No matter what the temperature of the mold and alloy as the pour is made, the mold and alloy must be at the freezing temperature when the alloy begins to freeze. For example, with Lyman #2, the alloy might be at 800F in the pot, the mold might be at 350 F, as the pour is made the alloy in the mold cools as the mold heats up, after the mold is removed from the spout both the alloy/bullet and the mold cool.
Thus, if the mold and bullet are at the same temperature when the bullet freezes, the temperature of the pot of alloy has no effect on the weight or dimensions of the bullet.
And, the room temperature bullet is always a smidgn smaller than the room temperature mold, the smidgn being the same for any alloy.
I think that this goes against my experience and that of others, but am beginning to suspect my memory. Perhaps an experiment is in order.
If I'm wrong on the synthesis above, please let me know!
Thanks;
joe brennan

[trk]

Lyman has printed that their blocks are made out of a semi cast iron semi steel called "meehanite".
...
joe brennan


Meehanite is a PROCESS not a type of iron. FWIW

[felix]

Yeah, it's true about the nomenclature on this board. It is becoming tailored very well to what we are all about, and it is becoming obvious that other folks, those having interest in cast bullets, are beginning to take heed. It's no different than any other self-serving congregation.

Joe, air is mostly nitrogen with 21 percent oxygen thrown in. Our nomenclature is the reverse in this instance, because we mean oxygen when we say air. Iron with lots of oxygen molecules implies lots of insulation because the oxygen is so dang large and extremely active when compared to nitrogen. The intent of fluxing is to get rid of the oxygen component from the melt, killing the insulation between the goodies we are interested in. This is where the Meehanite corporation comes into the picture. They discovered and/or perfected techniques to mix iron and other elements (copper for our purpose) that are tough to hold together after the mixing/cooling. This info in general can be found via the various industrial/professional rags dealing with alloys, machining, etc. ... felix

... felix

[TAWILDCATT]

I guess by now every one understands this thread but ME. I understand that
.001 is one thousand and .0001 would be ten one thousand.and .0003 would be three ten thousand.most tools measure to .001.so whats the point of all this.I may be getting old but I was a machinist for 60 yrs.
----:coffee: ----:Fire: ----:coffee:

[Firebird]

Further thinking on this issue and especially the point that not everything is at the same temperature leads to this observation - as the bullet solidifies from liquid to solid, it's not happening at the same instant all through the bullet. The bullet is going to solidify at the outside skin first as the heat transfers into the colder mould, then gradually solidify towards the inside of the bullet. What this process does to the density and final dimensions of the bullet is probably very different than what I have already said what has been already discussed on this thread. Liquid lead alloy is less dense than solid lead alloy; as the inner liquid lead solidifies it is going to shrink, this can either "pull in" the already solid outer shell of the bullet, reducing it's diameter; or cause porosity and voids inside the bullet. Higher pot temperatures could make this worse as the higher temperature lead alloy is going to be slightly less dense than colder liquid lead alloy, potentially leading to more shrinkage as it solidifies. Of course higher pot temperatures eventually also cause higher mold temperatures, so the bullets don't solidify as fast, leading to larger crystal structure and surface frosting; and also to the bullet shrinking more due to the higher internal temperature (resulting in lower density of the liquid lead in the middle of the bullet) when the outside solidifies.

And as far as great amounts of heat energy needing to be transferred as the liquid lead alloy cools and solidifies, lead has a VERY low specific heat (meaning that little energy is needed to raise it's temperature) and also a VERY low heat of fusion (means that very little heat is given up as it transitions from liquid to solid). So really not all that much energy is actually needed to heat & melt lead, or to be carried away as the lead cools and becomes solid again. This is in contrast to water, which has one of the highest specific heat values and also a very high heat of fusion. We are used to water taking a long time to heat and very long time to totally boil away, but actually we are only changing the temperature of the water by 130-150 degrees when we do this. Melting our lead alloys require changing it's temperature by 450-500 degrees and then having it transition from a solid to a liquid and this happens much faster than an equivalent pot of water boiling away despite the much higher temperature change happening.

[fourarmed]

Joe mentioned the difference in rate of radiation between a black iron mold and a light-colored aluminum mold. Without benefit of experiment, I am only speculating, but I would advance two hypotheses: 1. At the temperatures we're talking about, I doubt if the difference is significant., and 2. I would guess that heat loss from bullet molds is primarily convective rather than radiative. Unless of course you use the Bruce B technique, where conduction is dominant.

[joeb33050]

Meehanite is a PROCESS not a type of iron. FWIW

Meehanite is a type of iron. FWIW
joe brennan

The Metallurgy of MEEHANITE Nodular Iron

This range of cast irons is known under a variety of names - Nodular, SG iron, Ductile or Spheroidal Graphite iron. These materials possess strength and ductile properties of a different type to flake or grey cast irons, whilst maintaining comparable machining characteristics.

While providing mechanical properties similar to cast steel or malleable iron, nodular iron presents few of the problems met with either (founding, high heat treatment and distortion, seize and section limitations etc).

As nodular iron can be poured at temperatures much lower than for cast steel, cast finish and dimensional accuracy are improved.

[joeb33050]

I guess by now every one understands this thread but ME. I understand that
.001 is one thousand and .0001 would be ten one thousand.and .0003 would be three ten thousand.most tools measure to .001.so whats the point of all this.I may be getting old but I was a machinist for 60 yrs.
----:coffee: ----:Fire: ----:coffee:

For me the point is to try to understand one part of the CB game. Does pot temp affect bullet dimensions and weight?
joe b.

[joeb33050]

I don't know what this means, and I read it a lot. I understand the words, but don't understand if you think that pot temp affects bullet dimensions and weight.
My son went into this temperature variation bullet to mold to location in both.
Certainly temps vary place to place within the confines of the mold, certainly, at least big bullets harden or something from the outside-but I suspect that the whole bullet gets slushy first, then hardens.
And the whole casting cycle is ~ 30 seconds or less from pour to pour.
I can write left hand right hand charts for the process, imagine and describe hypothetical temperatures throughout the mold and in time-but does this mean that pot temp affects bullet wt.? Am I missing the point?
joe brennan





Further thinking on this issue and especially the point that not everything is at the same temperature leads to this observation - as the bullet solidifies from liquid to solid, it's not happening at the same instant all through the bullet. The bullet is going to solidify at the outside skin first as the heat transfers into the colder mould, then gradually solidify towards the inside of the bullet. What this process does to the density and final dimensions of the bullet is probably very different than what I have already said what has been already discussed on this thread. Liquid lead alloy is less dense than solid lead alloy; as the inner liquid lead solidifies it is going to shrink, this can either "pull in" the already solid outer shell of the bullet, reducing it's diameter; or cause porosity and voids inside the bullet. Higher pot temperatures could make this worse as the higher temperature lead alloy is going to be slightly less dense than colder liquid lead alloy, potentially leading to more shrinkage as it solidifies. Of course higher pot temperatures eventually also cause higher mold temperatures, so the bullets don't solidify as fast, leading to larger crystal structure and surface frosting; and also to the bullet shrinking more due to the higher internal temperature (resulting in lower density of the liquid lead in the middle of the bullet) when the outside solidifies.

And as far as great amounts of heat energy needing to be transferred as the liquid lead alloy cools and solidifies, lead has a VERY low specific heat (meaning that little energy is needed to raise it's temperature) and also a VERY low heat of fusion (means that very little heat is given up as it transitions from liquid to solid). So really not all that much energy is actually needed to heat & melt lead, or to be carried away as the lead cools and becomes solid again. This is in contrast to water, which has one of the highest specific heat values and also a very high heat of fusion. We are used to water taking a long time to heat and very long time to totally boil away, but actually we are only changing the temperature of the water by 130-150 degrees when we do this. Melting our lead alloys require changing it's temperature by 450-500 degrees and then having it transition from a solid to a liquid and this happens much faster than an equivalent pot of water boiling away despite the much higher temperature change happening.

[Bass Ackward]

From what I have seen over the years, how do you answer the question?

I have aluminum molds that goes tapered as the mold heats well enough to make good bullets. Because heat rises in the blocks, the base grows by .001 and the nose shrinks by .001 yielding a tapered bullet. This is in the same mold. But mold with only 4 cavities instead of six and turn the mold upside down after the sprue hardens for a 5 count to allow heat to travel up which is actually down to the nose and they are uniform again.

I have other aluminum molds that the hotter they get, the bigger the bullet they throw until they get way outta round. I have other aluminum molds that throw smaller bullets as they over heat.

I have brass molds that exhibit similar characteristics. Brass can be even worse than aluminum at first if it wasn't properly stress relieved. But once it shifts, it usually stays that way for all time meaning you are screwed.

Steel tends to the most stable which sounds good at first. But change the mix from low to no tin content, to a tin to high percentage tin content and then characteristics flip flops if you over heat. Aluminum then becomes the most stable because we are not running as high a temps cooking something out of tin mixes that ain't tin yet doesn't happen to tinless mixes. Unless we insist on frosting. Then the game is wide open again as stress comes back into the picture if it's there.

So if mold material and stress relief makes a difference. And the mix you are using makes a difference. Does the pot temp make any difference?

Old time casters and guys who need precision bullets for long range that are on the large size tend to ladle from a constant heat sourse and claim that they get better bullets than from a bottom pour. They said that decades ago and the trend continues. Wives tale or are they on to something? Even there, the amount of time for fluxing and variable casting rate will change the pot temp, so how do you prove it?

I purchased a box of machine made bullets that should have been produced with a constant rhythm that were unsized. Thus they had a machine rhythm and steady temperature of the mold, and they are slightly different with some being round and some not. So I guess you could say that the heat sourse there must have been a factor if the mold temp and the mix were the same.

I think this goes down as one of those things that you either accept the science or don't. But the reality is, with all that is going on, it doesn't matter to a hill of beans if something else I am doing is causing more variation.

[Firebird]

Joe

My point is that I don't think that the whole bullet goes solid at once - the hot liquid lead actually touching the colder mold will go solid first, then the bullet will go solid towards the inside of the bullet as heat is drawn out of the hotter lead and into the colder mold. No, I don't think that this takes a long time, probably less than a second but I really don't know and I'm not sure how to find out.
Since the inside of the bullet goes solid last, and lead shrinks slightly (like most everything else) when it goes from liquid to solid, the inside of the bullet is going to be pulling on the outside of the bullet; shrinking it very slightly. The hotter the lead starts out at, the more the temperature will vary between the inside and outside of the bullet as the lead goes solid and the more the inside lead will pull in on the outside lead as it cools and goes solid. Yes, some of the liquid lead from the sprue will get drawn down into the mold to "fill-in", but I think that the temperature variation will still put some stress into the solid bullet and cause it to shrink away from the mold walls a little, and the hotter the liquid lead starts out the more shrinkage will happen to the bullet..

[joeb33050]

Could be, I don't know. I think the alloy, most alloys we use, has a slushy stage. I think it's all slushy for a while, then probably the outside hardens first-maybe. But the temp of the whole thing must be down toward where it starts to freeze. I don't see a lot of time or shrinkage going on, but only experiments will tell.
joe brennan





Joe

My point is that I don't think that the whole bullet goes solid at once - the hot liquid lead actually touching the colder mold will go solid first, then the bullet will go solid towards the inside of the bullet as heat is drawn out of the hotter lead and into the colder mold. No, I don't think that this takes a long time, probably less than a second but I really don't know and I'm not sure how to find out.
Since the inside of the bullet goes solid last, and lead shrinks slightly (like most everything else) when it goes from liquid to solid, the inside of the bullet is going to be pulling on the outside of the bullet; shrinking it very slightly. The hotter the lead starts out at, the more the temperature will vary between the inside and outside of the bullet as the lead goes solid and the more the inside lead will pull in on the outside lead as it cools and goes solid. Yes, some of the liquid lead from the sprue will get drawn down into the mold to "fill-in", but I think that the temperature variation will still put some stress into the solid bullet and cause it to shrink away from the mold walls a little, and the hotter the liquid lead starts out the more shrinkage will happen to the bullet..

[leftiye]

Joe,
Haven't you ever made boolits with big holes in the base? We usually solve this by getting things hot enough that the sprue doesn't freeze so fast, and the sprue puddle is drawn into the boolit. Now what about when this cavity freezes over, and there is no place to draw more lead from? Doesn't the boolit shrink some? And finally, is it even necessary that there be a void to cause shrinkage? I think they all shrink. They all freeze from the outside, and the center does apply force pulling the outside inward. After all, what else can happen when the exterior is allready frozen and then the center freezes?

[montana_charlie]

I think they all shrink. They all freeze from the outside, and the center does apply force pulling the outside inward. After all, what else can happen when the exterior is allready frozen and then the center freezes?
I would speculate that the freezing starts at the nose and progresses upward...with alloy high in the cavity staying hot longer than alloy further down.

As for shrinkage, has anybody ever measured a hot bullet? I doubt it.
When the bullet is cold...and all of those molecules have collapsed to their 'normal' size...you can say that shrinkage has occurred.

Reheat that bullet in a 400 degree oven, and I bet it un-shrinks, some.

But, rather than pure speculation on the freezing thing, try this...

Get to casting good bullets, and note the amount of time it takes from when the cavity is full to just before the sprue freezes.

Then fill the cavity, leaving little or no sprue, and pop the mould open (over an empty pie pan, or something) at two thirds of the waiting time.

Do you get a shell of a bullet with a liquid middle?
Is it a solid nose with a runny rear?
Or do you get a puddle of slush which says the whole thing has to freeze in a single short moment?
CM

[joeb33050]

Joe,
Haven't you ever made boolits with big holes in the base? We usually solve this by getting things hot enough that the sprue doesn't freeze so fast, and the sprue puddle is drawn into the boolit. Now what about when this cavity freezes over, and there is no place to draw more lead from? Doesn't the boolit shrink some? And finally, is it even necessary that there be a void to cause shrinkage? I think they all shrink. They all freeze from the outside, and the center does apply force pulling the outside inward. After all, what else can happen when the exterior is allready frozen and then the center freezes?

No, all my bullets are perfect. And, I have this bridge for sale,...
I'm not disagreeing, I just don't know. You're not the only person who's talking about this. I'm still stuck with liquid, shrinking as temp goes down, slushy, shrinking as temp goes down, solid, shrinking as temp goes down. I'm not sure there's ever a solid outside and a liquid inside. Certainly something happens, we've all seen the sprue get that depression in the middle just before it hardens. And yes, they all shrink from hot and solid to room temp and solid.
I'm pretty well satisfied that variation in pot temp doesn't vary cool bullet dimensions or weight much, maybe not at all.
joe brennan

[44man]

I sure am not going to try and answer a slush question but if I am casting a large boolit and if I hold the ladle on for the required time I will see the lead stop entering the mold for a second, then the ladle level will suddenly go down. This can only mean the lead has hardened or turned to slush on the outside and near the nose first and shrunk enough to draw lead. When I remove the ladle, the sprue will only shrink like a drop of lead with almost no depression in the center. The sprue glazes from the outside towards the center first, then the whole sprue will turn color all over.
Now comes the question of a mystery mold. It is a friends .58 hollow base Minie'. I have done everything that can be done with it including cutting vent lines on the base plug. I have enlarged the block vents too. I have poured at every temp, from every angle and heighth, every speed and have even left the ladle on until the lead hardened in the nose. If I cast 200 in every way that can be done, there is a hollow in the lead above the base pin. I have even heated the pin before every boolit. Even holding the mold sideways and starting the pour as I slowly tip it up will leave the hole.
I have many other hollow base molds and none give me any trouble, just the one. Can any one say what is happening in this mold and to the lead?

[44man]

I tried something with the last batch of boolits. I overheated the mold. The first boolits were frosted good. I kept them separate. As the mold cooled, boolits stopped frosting so I kept them separate also. Then I cooled things more, lead and mold.
The first boolits would not touch the sizer and were lighter.
The next sized quite a bit and were near weight. The cooler cast were a tiny bit smaller and sized less. I did not measure them but let the way they sized show me.
Each mold will have one optimum lead and mold temp to cast the largest, perfect boolit. Go either way and the boolit changes. The worst is too hot. I do not see much difference when hot as I cast pure lead or near pure so the alloy will also change things. A cooler mold and lead will make the pure lead boolit a little smaller.
Not scientific, just by feel. I leave it up to all of you for the grain structure, etc.

[trk]

"I tried something with ...."

FINALLY, SOMEONE who DOES something and measures the result!

MANY THANKS, 44man for doing something EMPERICAL! Hot, warm and cold are good enough to prove the point. (I was dragging my feet on drilling a mould to put in the thermocouple - far to complicated to prove the BASIC assumption.)

[GSM]

PARTIAL QUOTE: I'm not sure there's ever a solid outside and a liquid inside.
joe brennan

If behavior is not completely dependent on object size, then there is a "solid outside and a liquid inside". Opening a hammer mould too soon proved that one for me.

fourarmed: Heat "loss" (transfer is probably a tighter term) from moulds should be both conductive and convective - the bullet, in contact with the mould, will conduct heat to the mould mass which will act as a heat sink, the mould will transfer heat to the surrounding atmosphere by convection, unless, of course, you grab a hold of it - then its back to conductive.

[leftiye]

All,
I don't think we should throw out all that is deduced (a LITTLE different from conjecture). After all, many so-called empirical "findings" are flawed too FWIW. And somehow, (as in the medical field) the "scientific" answers are so few and so slow in coming that if you wait for absolute proof you'll still be sucking your thumb at age 85.

In both cases too, they probably only constitute a basis point for further "conjecture." Further, those "conjectures" that are highly probably correct usually proceed forth from observed phenomena. The hard part is figuring it out in the first place, and designing an experiment to prove it may only be extra work done to soothe our self doubts, (and MAY only create further confusion). On the other hand, may we all always have some self doubt to prevent us from believing ourselves (to be right) all of the time.

[leftiye]

Montana,
Yes, I've done exactly what GSM describes with more than one boolit mold- ie. opened it before it was frozed. And, yes there was a shell of solid lead in one or both mold halves. I do think you're right about it freezing sooner from the nose of the cavity though. And also from the outside in. Another example of conjecture that isn't, we've done seen it happen.