Does a hotter melt = smaller boolits?

[crgaston]

Seems like it would, but I haven't seen anything in print one way or another.

What do you say?

[44man]

Seems like it would, but I haven't seen anything in print one way or another.

What do you say?
Yes. Cold makes a smaller boolit, just right makes the largest and when you get totally frosted, boolits shrink too much.
The enemy of consistent boolits is a pot that cycles over a wide temperature range.

[crgaston]

Thanks, 44man. Any downsides to frosty boolits? I was casting really hot, apparently, before I got a thermometer. Turned my pot down and my boolits grew. Those frosty boolits dropped much closer to the size I wanted them to be, and seem to shoot better, but I haven't done enough scientific testing to be able to say so for sure.

[Char-Gar]

It takes hot molten metal to be fluid enough to reach every nook and cranny and fill the mold cavity. Once the metal is hot enough to do a 100% fill that is as big as that bullet will get in that mold at that mold tempreture.

Now some alloys will cast larger or smaller depending on what is them and how much they shrink or expand when they are out of the mold cavity and cool.

So up to a point, hotter metal makes bigger bullets, but once that point is reached it is

All of this presumes the mold is up to casting tempreture and remains there fairly even. Molds that are to hot or too cold can also effect the size of cast bullets.

[mooman76]

Frosted bullets are fine as long as they are not so hot that they get distorted but that will be obvious. Some people don't like the looks of them but lifes too short to worry about getting the bullets perfect.

[geargnasher]

Bottom line is your frosty boolits from a hot mould/alloy will be smaller when you run them through the sizer than the ones that were cast from cooler mould/alloy, i.e. the shiny ones.

Gear

[theperfessor]

Regarding bullet sizes versus mold temperature - a lot of people agree with 44man, including some cast bullet manuals. Various people have offered rational explanations of why this occurs. With all due respects to all involved, until I see enough data from enough tests at different temperature ranges using different alloys I will keep my mind open. I don't disbelieve the anecdotal evidence, I just want to quantify what actually happens.

Since I was planning on making up some test molds for another purpose I have decided to test this phenomenon along the way. I am building a dual PID controller box. One controller will monitor and control the lead pot to maintain even temperature as 44man rightly points out. The other will have a thermocouple mounted in a 1/4-20 hole in a mold as an input and will control a hot plate to preheat the mold. I plan to make two molds, one aluminum and one malleable iron.

I want to quantify the proper melt temperature so that a mold of certain material will reach the minimum constant temperature needed for good bullets made of a certain alloy. Theoretically, if your alloy was the right temp and your mold was clean and preheated to the constant temperature point it should make good bullets the first pour.

The only additional work needed to test the bullet size/temperature phenomenon is to crank up the pot temperature and cast more test slugs. It will result in a lot more measurement work but I think its worth doing. Along the way I plan to record certain observations, such as how long it takes for the sprue puddle to set up and what the surface of the test slugs look like (shiny, frosted, etc.).

I'll post a thread about the PID box once I get it built and working. And then I'll publish the data for bullet size/mold temperature when I get done with that test. I'll wait for the data to explain what is happening and to what degree. Along the way there might be found a good explanation why.

[Marlin Hunter]

Prof. If you make the mold yourself, it might be a good idea to make different depth and width groove to see be sure the best mold temp fills out small (tumble lube) grooves as well as deep and wide groves.

There are 2 things happening with hotter casting.
(1) the mold cavity gets smaller as the metal expands due to heat.
(2) The hotter the lead the more it expands, and the more it shrinks when it cools.
It seems like the optimal temp is the one that gives complete fill with the least amount of heat.

You might also want to try the experiment with different amounts of tin to see if it will allow a lower temp for complete fill

[theperfessor]

I had planned to have some sort of "feature" such as a middle band that would allow me to see how the alloy fills out corners and edges. This is how I plan to determine minimum casting temperature - by definition as the temperature that gives complete fillout.

Actually mold cavities continue to get bigger due to expansion caused by heat. Which is why I want to know why people claim bullets shrink more when cast in a hot mold. Maybe they do, but I want to know what mechanisms actually cause that since the mold cavities grow larger with increased temperature. I've already tested that and published the results here.

The casting alloy freezes at the same temperature or range of temperatures whether it is cast in a hot mold or a cold one. And since the solidification temperature is the same, and the bullet undergoes the same temperature difference when it cools to room temperature, and the bullet cavity is bigger at higher temperatures, then how does the bullet end up smaller from a hot mold? If this is the case then there has to be something else going on here. I'd like to know what it is.

[crgaston]

Perfesser,
My personal theory is that the melt is less dense at a higher temp, and thus contracts more as it solidifies. As I said previously, though, I haven't done enough scintific testing to back this up.

[lwknight]

I could never tell that the melt temperature made any difference once the molds were hot.
Excessively hot alloy will slow your casting down because it heats up your molds more than just hot enough.
I have noticed that excessively hot molds seem to throw slightly smaller boolits. Guessing that it something to do with the very slow solidification in contrast to cooler molds.

And , yes the cavity does expand porportionately with the rest of the block as it heats up.

[sagacious]

...
Actually mold cavities continue to get bigger due to expansion caused by heat. Which is why I want to know why people claim bullets shrink more when cast in a hot mold. Maybe they do, but I want to know what mechanisms actually cause that since the mold cavities grow larger with increased temperature. I've already tested that and published the results here.
The above quoted assertion is absolutely correct. Once the entire mold is thoroughly heated to pouring temp, the cavities will be very slightly larger than when at room temp.


The casting alloy freezes at the same temperature or range of temperatures whether it is cast in a hot mold or a cold one. And since the solidification temperature is the same, and the bullet undergoes the same temperature difference when it cools to room temperature, and the bullet cavity is bigger at higher temperatures, then how does the bullet end up smaller from a hot mold? If this is the case then there has to be something else going on here. I'd like to know what it is.
Well, OK, here it is then. You almost hit on it yourself.

When lead is heated, like virtually any other liquid, it expands in volume. The hotter it is, the more it expands-- for example, this is precisely how a mercury thermometer works.

So, when you pour the cavities full of lead, you pour in a specific volume for that temperature. When you pour at higher temperature, you pour in metal that has expanded more, and thereby you pour in less metal by weight. That very slightly smaller quantity of lead still freezes to form an alloy that has the same density as when it was poured at a lower temp, and so the resulting castings will have a slightly smaller size and weight.

You can confirm this explanation by noting that the liquid density of lead is given at the melting point of pure lead, and that the coefficient of thermal expansion of lead is required to calculate the liquid density at higher temperatures. Note also that the coefficient of thermal expansion is greater for lead than for either alumimum or iron, and that the molten lead will always (necessarily) be higher than the mold temp. So the lead will expand more than the mold cavity expansion will 'correct' for, which means lighter, smaller bullets. Pencils down, physics lesson over. ;)

Now, empirically and personally, in my experience I have seen that bullets cast at very high temps are invariably smaller and lighter than bullets cast at a lower temp sufficient to give perfect fillout, and this effect is more noticeable in the larger calibers and heavier weights.

Hope this helps and makes sense. Good luck! :drinks:

[sagacious]

Yes. Cold makes a smaller boolit, just right makes the largest and when you get totally frosted, boolits shrink too much.
Precisely. Too cold often gives less-than-optimal fill-out and results in smaller castings. A temp just sufficient for perfect fill-out will give the highest weight and largest as-cast diameter. But much hotter makes for smaller bullets again, due to lead's thermal expansion.


The enemy of consistent boolits is a pot that cycles over a wide temperature range.
Precisely stated again. At it's most basic, I have long felt that mastery of accurate and consistent lead casting is mostly a matter of mastery over strict temperature control.

[303Guy]

sagacious

I agree with you (although I had to read your post twicw!)

Lead alloy in a boolit mold solidifies fron the outside in. But lead alloy does not just 'solidify'. It chrystalizes and a hot mold allows this to a greater extent. (Just try a hot melt cast into a cooler mold and see the difference). Once the casting has formed a semi-solid outer 'cast' it will only continue to 'shrink' as the interior cools, sometimes forming visible 'shallows' as the interior solidifies.

perfessor

I like the way you think!
I look forward to the results of your tests. (No small task you have taken on!)

[sagacious]

sagacious

I agree with you (although I had to read your post twicw!)

...Once the casting has formed a semi-solid outer 'cast' it will only continue to 'shrink' as the interior cools, sometimes forming visible 'shallows' as the interior solidifies.
...
Quite true. In a very large lead casting-- say few pounds-- those shrinkage cavities are large enough to deform and ruin the casting. I used to pour a lot of 3lb lead balls, and it was critical to pour at the lowest possible temp to avoid enormous shrinkage cavities. The larger the cavity volume and the higher the pouring temp, the more noticeable the shrinkage.

Sorry if I was unclear in my reply above. I try to keep it as concise as possible, but sometimes that compromises on clarity.

Cheers mate! :drinks:

[blikseme300]

The enemy of consistent boolits is a pot that cycles over a wide temperature range.

I must also agree with this statement. Added to this mix is the actual melt temperature and mold temperature. Then we also have the rate of cooling of the mold. Casting tempo varies according to the subjective change in the mold temperature as subjectively deduced from the boolit appearance. This is too imprecise.

The idea to add a thermocouple to the mold block to establish the best casting temperature range is an interesting idea. (Added this to my to-do list.) I already use a PID for my smelter and have noticed that the only other 2 variables I need to contend with now is the mold temperature and casting tempo.

An easy way to add temperature monitoring to the mold could be the use of something like this: http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=37772

I have one of these units and will see what the included thermocouple added to my different Lee 6-bangers tell me.

Bliksem

[Bret4207]

I've been an on and off fan of frosted boolits for years. I tended to cast with a hot mould (vs a hot alloy- 2 diff. things) to get good fillout and that sometimes got me frosty boolits. For a while I aimed for frosty boolits even, never had a problem with under sized boolits. I had perfect fillout and the boolits were all large enough to work for me.

So when I read that frosted boolits shrink more or otherwise produce smaller diameter boolits I'm a little skeptical. How much smaller? Is there a consistent ratio? And then there's the question of the boolit "growing" as it cures over a couple weeks. What effect does that have on the end product? Is there a consistent ratio there as well?

I have no answers for you. I know some moulds will produce a frosted boolit quite easily, other need to be abnormally hot to do it. I have yet to see a lightly frosted boolit that didn't perform as well as expected.

[lwknight]

Since not many people use the same alloys there will be all different kinds of experiences on this matter.
I use 92-2-6 and boolits that I started watching have not changed from cast time to date (about 2 weeks) I do not water quench either. If I start frosting, I slow down.
The 6% antimony does cast about 1/1000 bigger in 44 cal than WW cut with lead and tin added. FWIW if anything.

[c3d4b2]

I have decided to test this phenomenon along the way.

This is a great task that will be very informative.

The bullet size may be dependent on the alloy, mold temperature and alloy temperature. You can hold the alloy constant for the analysis. There may a dependence between the alloy temperature and the mold temperature. (As the alloy gets hotter the mould will become hotter.) It may be difficult to control the mould temperature. A factorial experiment set up would be the easiest method to analyze the mould temp and alloy temps.

[mold maker]

I would also like to see ambient temperature and with or without a fan noted, along with the other data.
I cast mostly outdoors in the Winter. Some cast indoors with a fan or not. Even more cast year round outside. This could easily make for a 70-80 degree initial cooling temperature differential, especially if a breeze is involved.

[303Guy]

Sorry if I was unclear ...Oh, it was my comprehension that wasn't working too well!:oops:


Since not many people use the same alloys there will be all different kinds of experiences on this matter.I'm finding out fast how differently different alloys can behave. (And how much there is to learn about casting!)

[Wayne Smith]

[QUOTE=sagacious;741248]When lead is heated, like virtually any other liquid, it expands in volume. The hotter it is, the more it expands-- for example, this is precisely how a mercury thermometer works.

So, when you pour the cavities full of lead, you pour in a specific volume for that temperature. When you pour at higher temperature, you pour in metal that has expanded more, and thereby you pour in less metal by weight. That very slightly smaller quantity of lead still freezes to form an alloy that has the same density as when it was poured at a lower temp, and so the resulting castings will have a slightly smaller size and weight.

In a closed system you are right. My molds are not a closed system, they draw more lead from the sprue puddle as the boolit solidifies.

I don't think this is an adequate explanation of the possible results of the Perfessor's experiment.

[44man]

Frosted boolits do no harm if they fit the gun but too hot with a TL boolit will ruin the boolit, even slight frosting does not make me happy.
My best boolits were made when I controlled the voltage but none of the controls lasted long before burning up. Even 1000 watt controls with large extra heat sinks failed and they are so expensive, it is cheaper to buy a new Lee pot.
Now for the goofy thing I found. I cut a cherry too small and the mold was a little under size so I put the mold in the freezer for a day and warmed the cherry. NOT A SINGLE SHAVING WAS REMOVED from the mold.
Then after casting some boolits I put the cherry back in the hot mold and it then removed a lot of aluminum so that my boolits are now perfect.
I figure it is because of two parts making the mold, not a hole in a solid piece. That means when you make a mold too hot, the cavity gets SMALLER. Now add an alloy that is too hot and has expanded and you have two things working to make a boolit smaller.
Reduce the heat and the mold will be larger and the lead more dense.
I have no real proof that a colder mold or colder alloy makes a smaller boolit from heat, only that they don't fill right. I will not make wrinkled boolits and never measure them because they go back in the pot. I think the lead cools so fast, size is affected.
Babore is the man to talk to, he has it correct. Make the cherry and mold larger because you can size the boolit but can not go the other way.
I do know a large boolit, cast at the right temp, and water dropped or heat treated will grow .001"-.002" with age. Smaller calibers grow less and an alloy with less antimony grows less.
With the vast differences in lead that we all use, it is hopeless trying to find an answer. Only with lab grade alloys can we find common ground.
I do know that using WW's to make my batches of alloy will change hardness from batch to batch and also accuracy. I get 5 shots in 5/16" at 50 yards from a revolver with one batch but the next batch will not touch it.
Due to alloy differences, my groups can NOT be shot all the time so it is a failing I live with. If I can hit a deer, it is OK.
My goal to a one hole group at 100 yards with cast is beyond my control and some alloys will prevent it at 25 yards.
I have learned to live fat and happy with the AVERAGE groups I shoot and to just cast at the temp that gives a nice boolit. I don't like wrinkled or frosted, only just right. My cheap Lee pot does a nice job. My old Lyman goes from lead setting up in the pot to too hot. My friends RCBS and Lyman's can not match the Lee either. Neither gets hot enough to fill a boolit, but they all get too cold.
I think a stove, a pot and a thermometer will work better. They can stick those thermostats where the sun don't shine.
We REALLY need voltage control.

[theperfessor]

Let me give a little background on why I want to do this test.

In ten to twelve years I plan to retire. I would like to have enough knowledge and equipment to make premium quality bullet molds to supplement my retirement. One of the main complaints I read about here all the time is that the bullets dropped from a particular mold come out the wrong size. I want someone to be able to order a bullet mold from me that will drop a bullet of a specific size using a specific alloy. I want to know what size cavity to make to accomplish this, and I want to be able to tell somebody what the minimum temperature is to cast good bullets with that alloy.

I did not originally plan to test bullet size versus a range of temperatures, I just wanted to determine the lowest alloy temperature to make good bullets (which I expect to vary according to alloy composition). But since some people might not be able to control temperatures that closely, when this question came up I thought I would include this aspect into my test.

Various mold makers base their mold sizes on information that may or may not be relevant to the materials contemporary bullet casters have available. Lyman bases their mold sizes on their #2 alloy, which includes linotype, a scarce commodity; RCBS bases theirs on a 90% Pb/10% Sn alloy - and what knowledgeable bullet caster uses more than 2-3% tin in anything? Custom mold makers base their sizes on a wide range of allloys, from pure lead for muzzleloaders to who-knows-what. None of the custom makers that I am aware of have published their results. They mostly do a good job at making molds the right size when you tell them what alloy you're using, but they haven't published their research for others to use.

Along the way, I intend to observe everything about the process, including sprue freezing time and bullet appearance. I also want to determine the mold stabilization (steady state) temperature for a mold of the size I plan to make compared to the alloy temperature. I want to know that an alloy temperature of X will heat one of my molds up to a steady state temperature Y and it takes Z amount of time for the sprue plate puddle to freeze, with the surface of the bullets having a particular appearance.

I don't expect to "control" the mold temperature, except during the preheat cycle, but the PID controller will give me the actual mold temperature during casting (I plan to unplug the hotplate used for mold preheat once I start casting).

As I have mentioned, there have been a number of observations made of this phenomenon, and a number of rational explanations offered for this; several are mentioned by various posters on this thread. Not doubting anybody here, but I want to test this for myself to be able to quantify what we're talking about here. (My pencil is not down yet; my physics lesson continues.)

I will have to limit my test somewhat simply from a time aspect, so I plan to conduct the test at ambient temperature (approximately 70F) in still air. These are the conditions I will be making and measuring bullet molds, and I want the data to reflect the actual manufacturing conditions under which I will be working.

As mentioned, I have a future purpose for my present madness. And I'm a learning junkie anyway; being a professor doesn't mean I know it all, far from it. It means I've learned the right questions to ask, and the right way to conduct tests to get the data necessary to determine the facts. And when I learn something, I share it with others, so we can all profit from it. That's my credo in life - test, discover, learn, share.

[44man]

Let me give a little background on why I want to do this test.

In ten to twelve years I plan to retire. I would like to have enough knowledge and equipment to make premium quality bullet molds to supplement my retirement. One of the main complaints I read about here all the time is that the bullets dropped from a particular mold come out the wrong size. I want someone to be able to order a bullet mold from me that will drop a bullet of a specific size using a specific alloy. I want to know what size cavity to make to accomplish this, and I want to be able to tell somebody what the minimum temperature is to cast good bullets with that alloy.

I did not originally plan to test bullet size versus a range of temperatures, I just wanted to determine the lowest alloy temperature to make good bullets (which I expect to vary according to alloy composition). But since some people might not be able to control temperatures that closely, when this question came up I thought I would include this aspect into my test.

Various mold makers base their mold sizes on information that may or may not be relevant to the materials contemporary bullet casters have available. Lyman bases their mold sizes on their #2 alloy, which includes linotype, a scarce commodity; RCBS bases theirs on a 90% Pb/10% Sn alloy - and what knowledgeable bullet caster uses more than 2-3% tin in anything? Custom mold makers base their sizes on a wide range of allloys, from pure lead for muzzleloaders to who-knows-what. None of the custom makers that I am aware of have published their results. They mostly do a good job at making molds the right size when you tell them what alloy you're using, but they haven't published their research for others to use.

Along the way, I intend to observe everything about the process, including sprue freezing time and bullet appearance. I also want to determine the mold stabilization (steady state) temperature for a mold of the size I plan to make compared to the alloy temperature. I want to know that an alloy temperature of X will heat one of my molds up to a steady state temperature Y and it takes Z amount of time for the sprue plate puddle to freeze, with the surface of the bullets having a particular appearance.

I don't expect to "control" the mold temperature, except during the preheat cycle, but the PID controller will give me the actual mold temperature during casting (I plan to unplug the hotplate used for mold preheat once I start casting).

As I have mentioned, there have been a number of observations made of this phenomenon, and a number of rational explanations offered for this; several are mentioned by various posters on this thread. Not doubting anybody here, but I want to test this for myself to be able to quantify what we're talking about here. (My pencil is not down yet; my physics lesson continues.)

I will have to limit my test somewhat simply from a time aspect, so I plan to conduct the test at ambient temperature (approximately 70F) in still air. These are the conditions I will be making and measuring bullet molds, and I want the data to reflect the actual manufacturing conditions under which I will be working.

As mentioned, I have a future purpose for my present madness. And I'm a learning junkie anyway; being a professor doesn't mean I know it all, far from it. It means I've learned the right questions to ask, and the right way to conduct tests to get the data necessary to determine the facts. And when I learn something, I share it with others, so we can all profit from it. That's my credo in life - test, discover, learn, share.
You have good ideas but learning from Babore, I will forever go a little larger and never try to hit the exact size with any alloy. None of us can match what you intend to set the molds with.
This has been the failing of all mold makers in the past and is repeated day after day at Lyman and RCBS along with many others. Nothing worse then a mold that makes boolits too small.

[lwknight]

One thing to clear up. I can cast into a 300 degree mold with any temperature alloy and get the same finish and I will test and prove true or not, but I think the drop size is the same.

If the mold is cold , you can actually get get good casts by casting really hot. Your mold will get entirely too hot rather fast too.

Once the mold is up to about 380 degrees you will have lightly frosted or as I describe it , satin finish. This is all due to slowing the solidification process.

In the thread " How much tin is needed " there is a very good post explaining more complications. :groner:

I am reasonably sure that drop size is most affected by mold temperature and alloy composition.

Lead shrinks and antimony actually grows as it crystalizes. And that helps control shrinkage if the cast is solidified quickly. Thats why dropped diamaters are slightly bigger with higher antimony. Albeit, the higher antimony boolits will weigh less.

I have no idea what tin does.

I know that you need enough tin to keep antimony alloyed, else it will gather at the top and oxidize to dross if you have a high content in the first place.

Now that I have thouroughly confused myself....

[sagacious]

...
In a closed system you are right. My molds are not a closed system, they draw more lead from the sprue puddle as the boolit solidifies.

I don't think this is an adequate explanation of the possible results of the Perfessor's experiment.
Not to be contentious at all, but the thermal coefficient of lead should offer adequate explanation of the observed results of a hotter melt giving smaller bullets.

Your statement above is actually the perfect proof of this phenomenon. If lead didn't shrink in volume as it cools, it wouldn't draw from the sprue puddle. If the lead puddle and the lead in the cavity stayed liquid until the temp of each was equalized, then your supposition above would be correct. However, the lead in the gate freezes long before the temps equalize, which can commonly result in less lead per volume in the cavity. It is basic foundry practice to pour at the minimum pouring temperature for exactly this reason.

This fact can easily be observed in experiment through noting that it's common for the sprue to solidify fully before the lead in the cavity has reached the same temp or degree of solidification. The sprue puddle cools faster because it's subject to radiative and convective cooling, and not just the conductive cooling that the casting is.

Hope this helps, good luck! :drinks:

[theperfessor]

I agree with that completely. Knowing the minimum size of a cavity is still useful information. The actual size of a cavity would of course be larger, to allow for sizing and uneven shrinkage.

[HORNET]

sagacious said:
If lead didn't expand as it cools, it wouldn't draw from the sprue puddle.
I'll disagree with that statement. If the lead didn't contract as it solidifies, it wouldn't draw from the sprue puddle. If it went the other way, it would push material OUT of the cavity.

[sagacious]

Let me give a little background on why I want to do this test.
...
No rationale needed for my benefit, Perfessor; I support your spirit of experimentation. Outside of school, what I learned about foundry and pouring practice I learned mostly the hard way, some of it the very hard way, and one would have to labor exhaustively to find a mistake or pitfall that I haven't stumbled into or suffered from yet. But, I have also learned a lot along the way, and I too strive for quantitative explanations for both successes and failures.

From a careful reading of your proposed experiment, I would very humbly offer that it seems unlikely that one can gather the specific data you list unless each sprue puddle is weighed, timed for solidification vs alloy, and measured for temp, it's mold contact area, etc, etc, etc. That is not intended to stifle your experiment in any way at all-- but like you, I'm simply sharing what I've experienced. I'm not speaking from theory when I say that a hotter melt can give smaller, lighter bullets, this is simply what I have seen and experienced.

I look forward to your test results and wish you the best of luck in your endeavors. :drinks:

[sagacious]

sagacious said:
I'll disagree with that statement. If the lead didn't contract as it solidifies, it wouldn't draw from the sprue puddle. If it went the other way, it would push material OUT of the cavity.

Absolutely correct, and thankyou for reading carefully and correcting my mistake in proofreading.

Yes, lead of course shrinks in volume as it cools. That's the heart of the matter in this discussion. Original reply corrected.

[theperfessor]

I note this question has brought forth a lot of discussion, which is all well and good. But until I get more information I will refrain from discussing what happens and why.

I will just conduct the test as detailed here and let the data speak for itself.

[runfiverun]

the mold temp issue has been touched on already.
but if you can control your mold to stay in the 350 375 range and hold our alloy in the 650-700 range with no wind disturbance and hold a consistent time frame from pour to pour you will make good boolits.
sometimes high humidity will increase the consistency of your weights also.
tin allows more alloy to break through the antimonial shell/crystals, tendrils, shield,branches however you see them, which helps the alloy fill out the mold better.
and does it at the lower alloy temps desired.

[theperfessor]

Runfiverun

Those are good temperatures to start with. Thanks for info.

[Blacksmith]

Perfessor
Give some thought to the cooling rates and resulting changes in grain size as the metal reaches the solidus.

Blacksmith

[semtav]

Since I read this post today, thought I'd do a quick test tonight to see if there was much difference.

Used 410663 410 grn mold. WW +2% tin.

Started out casting till the bullets filled good and temp was stable at 750 deg . Then cast a few more, and unplugged the mold. kept casting as the pot cooled until the bullets wouldn't fill good anymore. (about 600 deg)_

wound up with 14 bullets.

measuring them later, I didn't get a consistent increase or decrease in size. they varied all the way thru about +/- .0005 max.

will have to try casting bigger batches @ different temp but for now, will consider it irrelevent.
Hotter mold (resulting in a bigger cavity) may offset a hotter cast (more shrinkage.)

Biggest difference should be with hot lead and cold mold vs hot mold and cold lead.

but thats just my dime store phd theory.

[44man]

Since I read this post today, thought I'd do a quick test tonight to see if there was much difference.

Used 410663 410 grn mold. WW +2% tin.

Started out casting till the bullets filled good and temp was stable at 750 deg . Then cast a few more, and unplugged the mold. kept casting as the pot cooled until the bullets wouldn't fill good anymore. (about 600 deg)_

wound up with 14 bullets.

measuring them later, I didn't get a consistent increase or decrease in size. they varied all the way thru about +/- .0005 max.

will have to try casting bigger batches @ different temp but for now, will consider it irrelevent.
Hotter mold (resulting in a bigger cavity) may offset a hotter cast (more shrinkage.)

Biggest difference should be with hot lead and cold mold vs hot mold and cold lead.

but thats just my dime store phd theory.
A hotter mold will have a SMALLER cavity.

[44man]

Absolutely correct, and thankyou for reading carefully and correcting my mistake in proofreading.

Yes, lead of course shrinks in volume as it cools. That's the heart of the matter in this discussion. Original reply corrected.
This is why I use a ladle and hold it on the mold until the cooling boolit draws all the lead it needs from the ladle, not the cooling sprue.
You can see the lead in the ladle go down as the mold fills, stop and then go down again.
I will only have a tiny divot in the center of the sprue from the sprue itself shrinking.
Large boolits cast with a bottom pour will try to pull lead from a sprue that is cooling faster then the boolit.
I preheat my molds to 500* and the first boolit will be perfect and at the right pace I can dump a 20# pot without a reject. It is a relaxed pace and I use two, two cavity molds at the same time.

[sagacious]

...
I preheat my molds to 500* and the first boolit will be perfect and at the right pace I can dump a 20# pot without a reject. It is a relaxed pace and I use two, two cavity molds at the same time.
I do the same. I can often go a whole session without a reject when casting the larger calibers, and I'm fairly picky about quality and consistency. I'll not talk about it much, as I'm confident that I'd not be believed by some folks.

Again, I think your comment sums it up-- the best lead pourers I know make sure all the potential problems are addressed before they even pour the first bullet. That mindset is critical.

[sagacious]

A hotter mold will have a SMALLER cavity.

I must beg to offer a slight clarification here. A mold will have a smaller cavity as it warms up. But once the mold is thoroughly heated to a fairly consistent temperature from cavity surface to exterior mold surface, the cavity will then be slightly larger.

OK, but how can this be so, Sagacious? This is true of any metal cylinder during the heating cycle. Initially the cavity will be smaller, as the warming metal expands to compress the cavity, and once the metal mold temp has equalized, the entire cavity expands in size. And in fact, the entire mold expands in size.

The scale of effect is quite small on a bullet-mold sized object, but noticeably larger on, say, an artillery gun barrel, which provides us with an object example. In that case, the metal cylinder is the barrel, and the sighting calculation takes this effect into consideration-- for the first few shots of a cold gun, as the barrel interior heats, the metal expands inward (being prevented from expanding outward by the cooler barrel exterior), the bore diam is reduced very slightly and thus pressure, velocity, and range are all increased slightly. After the barrel is thoroughly warmed by repeated full-charge shots, the entire barrel expands, and thus the bore diam then expands slightly, but enough to affect the gunnery calculations. This is often called 'cold-gun effect' or the 'warmer effect.' Readers are invited to research this to their own satisfaction.

This is true from bullet molds to cannons to steel bridges. The mold cavity is simply a cylinder cut lengthwise, but the effect is the same.

Not arguing, just hoping to shed some light. :drinks:

[semtav]

Thanks Sag. that may explain a lot more of what I was seeing in the measurements. I was thinking only of a completely heated block of iron. We always heat an object and freeze a bushing when installing bushings in something. Never thought about what localized heat might do.

When you are using the core to heat the object that makes sense

Probably also explains why sometimes trying to remove a frozen bushing, heating just the area around it and cooling the bushing doesn't work.

[303Guy]

Due to alloy differences, my groups can NOT be shot all the time so it is a failing I live with. 44man

Coming from you that is indeed revealing information!

Of course it doesn't make finding the right combination of all the variable any easier but at least now I know the game isn't lost just because I failed this time!

Anyway, it wouldn't be any fun if it was too easy!

[44man]

I must beg to offer a slight clarification here. A mold will have a smaller cavity as it warms up. But once the mold is thoroughly heated to a fairly consistent temperature from cavity surface to exterior mold surface, the cavity will then be slightly larger.

OK, but how can this be so, Sagacious? This is true of any metal cylinder during the heating cycle. Initially the cavity will be smaller, as the warming metal expands to compress the cavity, and once the metal mold temp has equalized, the entire cavity expands in size. And in fact, the entire mold expands in size.

The scale of effect is quite small on a bullet-mold sized object, but noticeably larger on, say, an artillery gun barrel, which provides us with an object example. In that case, the metal cylinder is the barrel, and the sighting calculation takes this effect into consideration-- for the first few shots of a cold gun, as the barrel interior heats, the metal expands inward (being prevented from expanding outward by the cooler barrel exterior), the bore diam is reduced very slightly and thus pressure, velocity, and range are all increased slightly. After the barrel is thoroughly warmed by repeated full-charge shots, the entire barrel expands, and thus the bore diam then expands slightly, but enough to affect the gunnery calculations. This is often called 'cold-gun effect' or the 'warmer effect.' Readers are invited to research this to their own satisfaction.

This is true from bullet molds to cannons to steel bridges. The mold cavity is simply a cylinder cut lengthwise, but the effect is the same.

Not arguing, just hoping to shed some light. :drinks:
THE MOLD IS NOT A CYLINDER and that is where you make the mistake. Half the cavity is on the OUTSIDE of a block, it is not a hole through a block. When heated it is expanding in all directions. Not the same as a hole where the sides expand away from the hole.
I had the wrong thinking for a short time because I would freeze the mold, thinking the cavity would get smaller. In fact it got larger and a cherry would flop around in the cavity without cutting.
Cutting a cylinder in half turns things 180*.
If I cut a mold until finished with a cherry, then heat the mold and put the cherry back in, you would be surprised how much more metal I will cut out.

[lwknight]

Sagacious is not mistaken. All things expand porportionately. if you amount were not so infintecimally small, i could prove it. If the mold could expand to 100 feet long it would have bathtub sized cavities.
I really hate arguments like this when an experience shows contrast to theory and there has to be other factors that may not have been considered.
Its totally not personal. When everyone is honest and not just trying to be right, we all learn.
I'm not disrespecting anyone here as I and probably everyone else knows that is from observation and honesty, that the debaters speak.

[semtav]

I'll test one today. measure with a hole quage. check cold, then hot. should be measureable even if only .0001.
Interesting discussion tho.

[theperfessor]

Semtav

Go ahead and do test. I ran test using three molds. Checked size at room temp and after uniform heating in oven. Cavities always got bigger at higher temp as expected. I published data here, check Classics and Stickies. Never hurts to have a second round of tests to confirm facts.

Molds are so small that I don't put much credance in "cannon barrel effect" and it doesn't explain size issue for mold at stable, uniform temperature either.

I will maintain open mind and conduct test as described.

I finished CAD drawing of PID controller box last night and have almost all necessary hardware, plan to build unit over Christmas break.

[theperfessor]

Here is link to my original thread on mold size versus temperature:

http://www.castboolits.gunloads.com/showthread.php?t=60129

[44man]

More work needs to be done because nothing matches what I have found with re-cutting a cavity. Which direction does a cavity change? Does it get larger or smaller evenly or does it get oblong so you measure smaller one way but it is larger the other way?
I know the lead-lag of a cutter will make a mold larger at the parting line so a boolit is larger in that direction. After I re-cut a hot mold, the boolit is rounder. Is the cavity expanding one way and shrinking the other?
If you use a ball gauge to measure, you get a false measurement, only reading the small portion.
I do not profess to know what is going on but when I cut a mold that drops a boolit that is too small, I will heat the mold before re-cutting to enlarge the boolit and also to make a rounder boolit.
Unless you make your own molds, you can not see it for yourselves.
Yes, yes, yes, I know, heat a block with a hole in it and drop a frozen pin in the hole and it is welded together, never to be moved.
It is just not the same with half a hole on the edge. You need a tighter look at what you measure.

[BABore]

The only true way to get an answer is a setup with variable heat control, a way to measure the block temperatures real-time, and a CMM to measure several points on each block half circle.

I made a 4C mold to cast a 357 plinker boolit similar to Hornady's swaged SWC. I cast them from pure lead. Thinking I needed to run the pot and mold pretty hot, I casted a bunch of boolits that were egg shaped. They casted to the measured cavity and cherry size at the parting line. Opposite the parting line thay were 0.002" small. I later hand turned the cherry in each cavity thinking I might have missed a burr or something. No chips. Dropping the pot temp from 800 F to 700 F, and fan cooled the mold between cycles, produced good round boolits at size. I've seen this same thing on many molds.

[sagacious]

Sagacious is not mistaken. All things expand porportionately. if you amount were not so infintecimally small, i could prove it. If the mold could expand to 100 feet long it would have bathtub sized cavities.
I really hate arguments like this when an experience shows contrast to theory and there has to be other factors that may not have been considered.
Its totally not personal. When everyone is honest and not just trying to be right, we all learn.
I'm not disrespecting anyone here as I and probably everyone else knows that is from observation and honesty, that the debaters speak.
Here is where I must thank you for your sagacity. I have no desire to be "right" here, only to try to shed some light on a question that is not quiet as vexing and insoluable as it might seem.

Let me be clear that I mean no disrespect in saying this, but I often find that as some discussions progress, the various sides simply harden their opinions against fact and rationality-- as though mere strength of conviction was something to offer in a discussion.

Myself, I learn more when I'm shown to be mistaken. I learn nothing when I'm correct in my assetion-- but others may learn in that instance. Every thread provides a teachable moment. In this case, the thermal expansion of metal is something that we should all be able to get our minds around, once we wade through the variables and prejudices that can confuse our perceptions.

[sagacious]

More work needs to be done because nothing matches what I have found with re-cutting a cavity. Which direction does a cavity change? Does it get larger or smaller evenly or does it get oblong so you measure smaller one way but it is larger the other way?
44man,
Please allow me to comment further without appearing antagonistic. I make molds myself, from bullet molds to swage dies to molds for jewelry to machine parts.

I know exactly what you're saying. The steel cherry or mold blocks will only expand an infinitesimal amount upon heating/cooling. Not nearly enough to affect cutting the small mold cavity. This is why railroad tracks or steel bridges only need a tiny expansion joint for 100' linear feet of steel-- the expansion is there, and must be addressed, but the linear expansion is small even for that great amount of steel.


I know the lead-lag of a cutter will make a mold larger at the parting line so a boolit is larger in that direction. After I re-cut a hot mold, the boolit is rounder. Is the cavity expanding one way and shrinking the other?
If you use a ball gauge to measure, you get a false measurement, only reading the small portion.
Absolutely correct, one can get a false reading. To answer your question strictly, the mold expansion is proportional to the thickness of the metal in that area. Thicker areas expand more. But for the purposes of this discussion and to help clarify one's mental picture, the mold blocks and cavities can be visualized as expanding essentially equally in all directions. I hope you see what I'm saying.


I do not profess to know what is going on but when I cut a mold that drops a boolit that is too small, I will heat the mold before re-cutting to enlarge the boolit and also to make a rounder boolit.
Unless you make your own molds, you can not see it for yourselves.
Yes, yes, yes, I know, heat a block with a hole in it and drop a frozen pin in the hole and it is welded together, never to be moved.
It is just not the same with half a hole on the edge. You need a tighter look at what you measure.
It's the same for a hole on the edge. A round hole, cylinder, square, on the edge or in the center, through-hole or blind hole-- doesn't matter in this case. A hole becomes larger in diameter when heated, and half a hole gets bigger likewise. What you're seeing is correct, recutting the cavity will often produce a truer cut, but as you know, there are all kinds of things that conspire to make holes go out-of-round while cutting, and a final recutting often adresses this fact. Once the blocks are warmed through, the cavity has expanded in all directions.

Hope this helps, just trying to carry the discussion forward. Cheers. :drinks:

[sagacious]

...
I made a 4C mold to cast a 357 plinker boolit similar to Hornady's swaged SWC. I cast them from pure lead. Thinking I needed to run the pot and mold pretty hot, I casted a bunch of boolits that were egg shaped. They casted to the measured cavity and cherry size at the parting line. Opposite the parting line thay were 0.002" small. I later hand turned the cherry in each cavity thinking I might have missed a burr or something. No chips. Dropping the pot temp from 800 F to 700 F, and fan cooled the mold between cycles, produced good round boolits at size. I've seen this same thing on many molds.

Your observation matches mine, and offers a good example for this discussion. I have seen the same, especially with pure lead. The thermally-induced shrinkage effect is most noticeable with pure lead.

This effect will usually become less noticeable as alloy percentage increases. In general, pure metals expand more upon melting, and contract more upon freezing-- as compared to alloys.

[semtav]

took my 410663 and set the hole guage so it was snug 90 deg to the part line with the mold cold. (45-50 deg)

put it on the hot plate and left it there while I cast some bullets with another mold. (at least 45 min) Not sure of the final temp but fairly hot.

when I was done, I tried to insert the hole guage. wouldn't go in. had to reduce it a little bit.

I tried to measure the before and after, didn't get a good reading, but Pretty sure it was less than .0005.

It was done with normal pressure on the handles. ( I thought about using C clamps, and may still sometime)

so my first test, showed the mold cavity did actually shrink (in one direction) as it got hotter.

This was only one test and not indicative of what others may find.

[44man]

There is something to wonder about. Drill holes in metal at different positions in the block, center, close to the edge and half a hole on the edge. What kind of expansion or contraction does each have at every point on the hole?
Semtav gets the same results I do in that the cavity gets smaller when heated.

[sagacious]

...
so my first test, showed the mold cavity did actually shrink (in one direction) as it got hotter.
...
Good test. Those results may also indicate that the blocks warped due to being placed on a hot surface, or from residual stresses during manufacture, leaving the cavities out-of-round to the minor degree you measured. This seems quite possible.

Just for kicks, it might also have been interesting to have measured the mold you were casting with-- the one that was heated from the inside, and that we can be sure was heated thoroughly enough to give good fillout (a practical indicator of uniform heating).

The Perfessor's experiments on this are also interesting. Whatever the results, and even whatever the disparity in results, it's good to see folks taking the Socratic method, and testing theory against experience. That's where the rubber meets the road.

[sagacious]

There is something to wonder about. Drill holes in metal at different positions in the block, center, close to the edge and half a hole on the edge. What kind of expansion or contraction does each have at every point on the hole?
Semtav gets the same results I do in that the cavity gets smaller when heated.

Would a heat-expanded bushing instead decrease in size if it were cut into two halves-- as a mold cavity is? :rolleyes: Just joshing ya.

But your test parameters are a good and commendable approach here. The only point I might stress is that non-uniform heating is very likely to produce different (even opposite) results than uniform heating.

Good luck, keep on keepin on. :drinks:

[semtav]

Good test. Those results may also indicate that the blocks warped due to being placed on a hot surface, or from residual stresses during manufacture, leaving the cavities out-of-round to the minor degree you measured. This seems quite possible.



I only measured in one direction for the first test, because I wanted to leave the small hole guage exactly like I set it. in case I didn't get good measurements with the micrometer.

My mold is slightly out of round, and when I set the hole guage snug at the 90 deg point, it was still loose at the parting lines.

tomorrow night, I will try it at the parting lines only and see if the results are the same.

I'm only capable of keeping track of one test at a time.

for all I know, I left the guage too close to the pot, and it swelled .0001 while casting

[lwknight]

Sagacious, I think you just hit on the answer to the missing factor of the arguement.
If a block of metal is stressed and part is cut away while under self stress, unpredictable things will result.
This may explain part of 44man's position on the matter of experience.

[theperfessor]

If you will read my original post testing this you will see that the Lyman mold did actually shrink slightly (0.0005") in one axis, which would be enough to be "feelable" using a small hole leaf type gauge. But you will also note that the same mold expanded 0.0015" in the perpendicular direction, thus increasing the overall volume of the cavity.

Please note something else. I clearly stated the basic premise of the test. I accurately described the items tested and the time/temperature parameters. I also identified the measuring tools and level of resolution.

None of the data I collected contradicts anything that has been known and accepted for a long time concerning uniform (equally in all directions) expansion of metallic materials when going from one uniform temperature to another, at least as having the largest gross effect on size changes.

There are some localized and/or non-uniform conditions that can cause short and long term size changes that are great enough to overcome the gross effects of uniform volumetric expansion.

1. In ferrous materials, untransformed martensite will revert to ferrite at any temperature greater than its tempering temperature. The difference in crystal structure and the relief of localized thermal stresses will cause long term warpage.

2. Extruded/rolled materials can have very high surface to interior stresses caused by the extrusion/rolling process. Mechanically relieving these imbalanced stresses during machining can cause short and long term warpage. Thermal stress relieving prevents this.

3. Non uniform temperatures can cause non uniform expansion, i.e. the cold exterior/hot interior effect. My get feeling is that a typical mold at a stable temperature, caused by the melt temperature and casting rate, will have a uniform enough temperature for all practical purposes.

Guys, I took twenty four measurements. There were twelve size comparisons. There was exactly ONE case where the value for a measurement taken in ONE direction showed shrinkage. And the expansion in the other axis of the same cavity was three times greater than the perpendicular shrinkage.

It doesn't surprise me that observations of size changes based on single observations or measurements may sometime show the contrary example. It wouldn't surprise me either if somebody set up a test at least as thoroughly as I did and got data showing an average increase in size consistent with long accepted theory and practice with a limited number of contrary examples, which can be explained by many other effects.

I'm not a disbeliever in other's experiences, but I am not ready to toss out my belief in uniform thermal expansion making holes bigger. No matter where they are.

[303Guy]

I have just cast a few boolits and am astounded at the difference in as cast size. Same alloy, same mold, same pot temperature (more or less).

Warm mold was casting frosted boolits.
Very hot mold took a minute or two for the sprew puddle to freeze.

Base shank with warm mold - 6.45mm/.2539"
Base shank with very hot mold - 6.02mm/.2370"

Nose shank actually tighter on hot mold sample!

Nose shank with warm mold - 6.03mm/.2374"
Nose shank with very hot mold - 6.04mm/.2378"

Base shank with very hot mold - 6.02mm/.2370" (Mold size .258)
Nose shank with very hot mold - 6.04mm/.2378" (Mold size .2375?)

Go figure!:shock: