What Causes Boolit Shrinkage

[AriM]

The more I seem to think I know what causes shrinkage, the more my efforts prove me wrong. I have read some books, and asked some questions and done some tests. I still (on occasion) get results that leave me a bit puzzled.....so I am reaching out to this wonderful community, of skilled, patient and experienced folks.......is it possible that something other than alloy make-up and heat affect shrinkage?

[ETG]

There is no correct answer to the poll. Most correct would be the last except for the unknown.

[Charlie Sometimes]

Why don't sheep shrink when they get wet?
They are wearing wool, right?
There is a factor involved that we can't obviously see.

Shrinkage is related to all the elements involved and forces of natural law- it's just the way it is!

I once asked one of my science teachers "Why does it do that?" I was told I asked too many questions!

[AriM]

There is no correct answer to the poll. Most correct would be the last except for the unknown.

so you assume that we know everything related to the phenomenon of shrinkage? wow, that seems a bit close minded....not sure I can get on board with you on that one....

science is nothing more than theory....there is no absolute

not trying to be a dick, but I can't get on the same page with this response....it answers no questions....just makes a statement, that we know everything there is to know

[AriM]

Why don't sheep shrink when they get wet?
They are wearing wool, right?
There is a factor involved that we can't obviously see.

Shrinkage is related to all the elements involved and forces of natural law- it's just the way it is!

I once asked one of my science teachers "Why does it do that?" I was told I asked too many questions!

yes, I am on the same page as you friend....maybe we could try to quantify some of those unknowns....we are all smart folks (???)....

I can subscribe to the school, that more or less lead, changes density and cooling...so that will effect size

also I can accept that temperature can be a cause....they are both related....

but what about those pesky unknowns??

it seems that there is more to it than just alloy chemistry and heat....MUCH MORE!!!

[Charlie Sometimes]

Could it be the way the atoms align at that the atomic level?
Crystals form and we can see that- sometimes smaller and sometimes larger, depending on the temperature and how slowly things cool off.
It stands to reason that there could be more room for expansion or contraction depending on the composition of the melt.
Why does heat treatment work? It's warm enough for the atoms to be able to realign themselves into something more durable- again depending on the ingredients.

Electricity is all theory too- but we know it works, and use the H out of it!

This is the same way, like most religions, I guess- you just have to take it on FAITH.

[AriM]

Could it be the way the atoms align at that the atomic level?
Crystals form and we can see that- sometimes smaller and sometimes larger, depending on the temperature and how slowly things cool off.
It stands to reason that there could be more room for expansion or contraction depending on the composition of the melt.
Why does heat treatment work? It's warm enough for the atoms to be able to realign themselves into something more durable- again depending on the ingredients.

Electricity is all theory too- but we know it works, and use the H out of it!

This is the same way, like most religions, I guess- you just have to take it on FAITH.

wow, big earthquake just hit us.....SCARY one !!! sheesh

ok so I am on board with the atomic alignment theory. I makes the most sense with high antimony content alloy. The antimony does not become fully solvent in the melt. These larger crystaline structures cause more rapid cooling, which allows for less shrinkage. That is a given. I would assume most of us know that.

My theory about heat treatment, is that it's just a surface treatment. If we were to dig into the core, we would find a softer alloy.

I believe the reason for this, is that the hotter portions of the melt bind in the center of the casting. The antimony and other materials find their way to the surface. This would explain surface heat treating also. Since lead does not respond to heat treatment. Therefore the metals that do respond to quenching are on the outside of the boolit, this is why only the outer layers of the boolit are harder. As you get into the core you find softer material.

Is this due to more rapid cooling of the outer layer, or metal oxidation? That is beyond my ability to test....

[Charlie Sometimes]

Granted- an earth moving subject!

Now, I'm no expert metallurgist or anything- and this could get way out of my understanding pretty fast.......

All of this is beyond anybody to test, IMHO.
You can't test the core of a bullet without effecting how it behaves, so how was it or wasn't it before you "looked".

"Heat treatment" is not just a surface application, but can be. Compare steel to our alloy, and iron to the lead. Iron won't heat treat without the carbon, and other additives. Case hardening is a surface treatment because you are adding the carbon to the surface of the metal only (over time with heat and molecular contact). An alloy of high carbon steel (such as used in knife blades or saws) will have it throughout the blade.

Heat treatment is performed on boolits (for most people) for one hour then they quench.
If you would wait longer, say several more hours, then I think the center would be as hard as the outside, because all of the molecules would have time to distribute themselves equally and evenly size themselves. BUT, how long would that really take, and why would you need to do that, when what we are doing serves the purpose at the surface. (rhyme!)

In casting a boolit, you want the mold to be completely full before any of it solidifies, and I would hardly think that the core would be softer. If you watch your sprue cool, you will see it shrink and pull additional metal into the cavity, so it has to have the same composition as the rest of boolit. The longer it is liquid, the better the fill, given proper venting- but you don't want to wait all day for that to happen.

This is also part of that process that you are trying to figure out- anything hot will take up more space than something cold due to the expansion of molecules. If hot enough, it will convert to a gaseous state and expand further, unless you compress it. (Could we vaporize our elements, blend them, compress them, and then cool them back into "The Best Alloy Ever"?)

Metals just exist at these temperatures in our environment, and look like other things on other planets. It's not rocket science, so don't make it any more difficult- just have fun!

Gee, I didn't know I was going to have to write a dissertation!
I'd better get a good grade.........

[AriM]

Granted- an earth moving subject!

Now, I'm no expert metallurgist or anything- and this could get way out of my understanding pretty fast.......

All of this is beyond anybody to test, IMHO.
You can't test the core of a bullet without effecting how it behaves, so how was it or wasn't it before you "looked".

"Heat treatment" is not just a surface application, but can be. Compare steel to our alloy, and iron to the lead. Iron won't heat treat without the carbon, and other additives. Case hardening is a surface treatment because you are adding the carbon to the surface of the metal only (over time with heat and molecular contact). An alloy of high carbon steel (such as used in knife blades or saws) will have it throughout the blade.

Heat treatment is performed on boolits (for most people) for one hour then they quench.
If you would wait longer, say several more hours, then I think the center would be as hard as the outside, because all of the molecules would have time to distribute themselves equally and evenly size themselves. BUT, how long would that really take, and why would you need to do that, when what we are doing serves the purpose at the surface. (rhyme!)

In casting a boolit, you want the mold to be completely full before any of it solidifies, and I would hardly think that the core would be softer. If you watch your sprue cool, you will see it shrink and pull additional metal into the cavity, so it has to have the same composition as the rest of boolit. The longer it is liquid, the better the fill, given proper venting- but you don't want to wait all day for that to happen.

This is also part of that process that you are trying to figure out- anything hot will take up more space than something cold due to the expansion of molecules. If hot enough, it will convert to a gaseous state and expand further, unless you compress it. (Could we vaporize our elements, blend them, compress them, and then cool them back into "The Best Alloy Ever"?)

Metals just exist at these temperatures in our environment, and look like other things on other planets. Have faith, ye who art full of doubt! It's not rocket science, so don't make it any more difficult- just have fun!

Gee, I didn't know I was going to have to write a dissertation!
I'd better get a good grade.........

it being difficult and "rocket science" makes it fun for me


I think anything that leads to us having a further understanding and leads to better consistency, is good sport....and lot's of fun in the process....


I have noticed some things, in the course of casting that conflict with some of these experiences of yours.....but again, all we can do is observe and report. as you say, we have no way of testing this stuff.

maybe I should take some classes on the subject. then I can be more helpful to the community and ask less questions. Of course that is what i am doing with this thread, asking questions.

no line in the sand here.....




oh also B-

which ain't bad....since neither of us can back any of this up with data

[Charlie Sometimes]

It don't hurt to ask questions.
It's just sometimes you don't get answers.
This is just the way I see things, albeit condensed a good bit.

They say the only stupid question is the one that goes unasked.
The only question that goes unanswered is the one not asked, too.

I know there are a few metallurgist types on here.
Maybe they can fill in more blanks for ya, or correct me if I am wrong in any way.

What observations of yours "conflict" with what I have said?


B minus? Must be grading on a curve.........

[KYCaster]

so you assume that we know everything related to the phenomenon of shrinkage? wow, that seems a bit close minded....not sure I can get on board with you on that one....

science is nothing more than theory....there is no absolute

not trying to be a dick, but I can't get on the same page with this response....it answers no questions....just makes a statement, that we know everything there is to know

Not close minded at all.

A theory that's been proven through experimentation to be predictable and repeatable is no longer a theory, it is a law. Like the difference between gravity and relativity; one's a law and the other is a theory.

Thermal expansion of metals has been studied and understood for many centuries. It is both repeatable and predictable.

yes, I am on the same page as you friend....maybe we could try to quantify some of those unknowns....we are all smart folks (???)....

I can subscribe to the school, that more or less lead, changes density and cooling...so that will effect size

also I can accept that temperature can be a cause....they are both related....

but what about those pesky unknowns??

it seems that there is more to it than just alloy chemistry and heat....MUCH MORE!!!

Nooooooo....alloy chemistry and heat is pretty much all there is to it.

wow, big earthquake just hit us.....SCARY one !!! sheesh

ok so I am on board with the atomic alignment theory. I makes the most sense with high antimony content alloy. The antimony does not become fully solvent in the melt. These larger crystaline structures cause more rapid cooling, which allows for less shrinkage. That is a given. I would assume most of us know that. I, for one, don't know that. From what I've read (and my experience doesn't contradict it) antimony, in the amounts we're concerned with, does completely dissolve in lead. And you'll have to prove to me that size or shape of crystal will cause it to cool more rapidly, or how the rate of cooling will affect the total shrinkage.

My theory about heat treatment, is that it's just a surface treatment. If we were to dig into the core, we would find a softer alloy. Properly heat treated, the hardness will be through and through, but this could vary slightly with very large parts.

I believe the reason for this, is that the hotter portions of the melt bind in the center of the casting. The antimony and other materials find their way to the surface. This would explain surface heat treating also. Since lead does not respond to heat treatment. Therefore the metals that do respond to quenching are on the outside of the boolit, this is why only the outer layers of the boolit are harder. As you get into the core you find softer material. The hardness at the core of the boolit will be essentially the same as the surface. I've seen no evidence to show that the alloy composition at the surface of the boolit is any different than at the core.

Is this due to more rapid cooling of the outer layer, or metal oxidation? That is beyond my ability to test....

This subject has been discussed here several times before. A search should turn up quite a bit of info. Also, a Google search for "precipitation hardening" will give you some insight into how heat treating actually works in iron alloys. Our lead alloys act very similar.

Jerry


Edit to add: Sorry, I got off onto heat treating.

For any particular alloy the thermal expansion and contraction will be repeatable and predictable. For each degree of temperature rise there will be a certain amount of expansion. Change the alloy and the rate of expansion may change, but for that alloy the thermal expansion will also be consistent. (normally expressed as "thousandths of an inch[of expansion] per inch[of part dimention] per degree")

If the shrinkage of your boolits isn't consistent then your casting method isn't consistent. Keep the alloy consistent, the metal temp consistent and the mold temp consistent and the shrinkage will be consistent.

[AriM]

Just a suggestion intended to promote better discussion, from a dialectic standpoint.

The statements quoted above are worded in a form known as "poisoning the well." I'm not suggesting that this is in any way intentional; I am just pointing it out.

What that means is that the statements are worded such that they have a strong tendancy to affect all following responses in a way that tends to invalidate any that might contradict with the original premise. This invariably leads to a discussion slanted strongly in one direction. It is likely that many knowledgeable folks will immediately recognize this pattern and refrain from entering the discussion. In this manner, the original premise strengthens itelf, and the intellectual integrity-- and general utility-- of the discussion suffers.

One might want to start a thread asking for opinions without first stating that he has "asked all the questions" (possible, but improbable), "read all the books" (very unlikely), and "done all the tests" (exceedingly unlikely). These statements set the petitioner as both expert and sole arbitrator, and consign all possible explanations to mysticism.

The answers to the original questions can be found in any first-year metallurgy schoolbook, any number of which can be obtained online, in used condition for a low price. It's interesting stuff.

Not preaching, just trying to shed some light. Best of luck.

I will modify the initial post. the loading of the question is, very intentional however.

I have found answers to the question, in basic metallurgy queries. Yet I am finding them to be somewhat inconsistent. The main purpose of this post, is to try and determine a specific problem that I am having. I have a mould, that seems to behave completely different than all of my other moulds. The only difference (they are all the same cal.) is that this specific mould is based on a different material (brass). i am trying very hard to understand why it is giving me un-usable results. I am also trying very hard not to make mention of the mould or it's source, as I believe the problem is something I am doing, and not the mold maker.

So far the problem I am having contradicts everything I think i know about casting. which I will freely admit, is nowhere near what most of you guys know. I can only base my knowledge on what I have experienced, through observation, trial and error, and here-say/reading.

I will modify the initial post though. I does make some blanket statements and assumptions, that are not accurate.

Thanks for the tip....

[AriM]

Not close minded at all.

A theory that's been proven through experimentation to be predictable and repeatable is no longer a theory, it is a law. Like the difference between gravity and relativity; one's a law and the other is a theory.

Thermal expansion of metals has been studied and understood for many centuries. It is both repeatable and predictable.



Nooooooo....alloy chemistry and heat is pretty much all there is to it.





This subject has been discussed here several times before. A search should turn up quite a bit of info. Also, a Google search for "precipitation hardening" will give you some insight into how heat treating actually works in iron alloys. Our lead alloys act very similar.

Jerry


Edit to add: Sorry, I got off onto heat treating.

For any particular alloy the thermal expansion and contraction will be repeatable and predictable. For each degree of temperature rise there will be a certain amount of expansion. Change the alloy and the rate of expansion may change, but for that alloy the thermal expansion will also be consistent. (normally expressed as "thousandths of an inch[of expansion] per inch[of part dimention] per degree")

If the shrinkage of your boolits isn't consistent then your casting method isn't consistent. Keep the alloy consistent, the metal temp consistent and the mold temp consistent and the shrinkage will be consistent.

ahhhh but herein lies my problem.....some of my boolits, out of one specific mould are consistently undersized.....so I am thinking something other than regulating alloy make-up and casting temperature is causing this....

I don't want to mention the mould maker, because I don't think the problem is his moulds.....he has sent me 2 already...and they both exhibit the same behavior....which is contrary to other moulds I own

I was trying really hard to not make mention of this, but maybe me beating around the bush, has caused some confusion....I want very much, to NOT mention the mold maker.....I would like to first rule out (with a certain degree of certainty) that the problem is or is not me....

[AriM]

on a side note.....why is everyone so willing to take everything as being law? I mean with this approach, no advancements would have ever come about....I think i should be encouraged to question some of these "laws".....maybe we can all discover something helpful, together....

I started a thread about developing a new lube, some months ago. I was immediatly attacked by a few individuals. They claimed that everything there is to know about lube has been discovered, and that i was naive and foolish for trying anything new....

I then went ahead with the project anyhow. i developed something unique and different. After I posted my results, everyone seemed interested in the new discovery....

I find this strange....to discourage someone from questioning things, and then to ask them to share their findings once a breakthrough is made....

maybe I am in the wrong place.....I don't even pretend to know what I am doing, but to cut me off before I have the chance to discover, seems counterproductive, anti-progress and somewhat anti-american.....

I am not pointing fingers, because those who find contempt for my lack of understanding, already know who they are....

thanks to everyone who has been helpful here at CB....I like this place very much and am doing my best to contribute and understand....

[RobS]

AriM:

Well you see there is a way for a law to be changed and it is by the proof of a new one

The scientific method is based on:
Ask a Question
Do Background Research
Construct a Hypothesis
Test Your Hypothesis by Doing an Experiment
Analyze Your Data and Draw a Conclusion
Communicate Your Results

Some here are a bit fussy about things and feel that "this" or "that" is absolute. I am along the range that there could be change and many times there is change. It is all how a person words things that yield a better understanding and acceptance on this forum. Do not get me wrong here as this forum is the best wealth of knowledge for a cast bullet enthusiast.

I use for example a lot of:
probably
should
in my opinion
this is what I have discovered
this is what works for me
take it for what it's worth
I believe
among a variety of other neutral terms

The question you propose is good one which has many responses here on the forum and it is also another debate which ruffles feathers. Another classic is the debate over hard and soft bullets etc. I, like you, and many others here have had one constant to casting and reloading..............things are always the same and yet always changing.

I enjoy reading of people here who have initiative to stand outside the box and it is even more inviting to read of those who have practical knowledge of their actual real life data. You mentioned that when you proposed the thought of a different lube that you were shot down (no pun intended) and it was only when you had experiences and data collected with it that people opened up and took more interest once you posted your results.

Your lube experience is a mockup of the scientific method and with it comes the understanding and acceptance of others.

[montana_charlie]

I don't want to mention the mould maker, because I don't think the problem is his moulds.....he has sent me 2 already...and they both exhibit the same behavior....which is contrary to other moulds I own.

When faced with something that seems inexplicable with things I have been taught, I turn to simple logic for a possible answer.

When I drop a Stanley 16 ounce hammer on my toe, it hurts. Every American-made 16 ounce hammer I have dropped causes the same amount of pain.
But, I have two Chinese hammers that are marked 16 ounce. Both of them make my toe hurt more.
Logic would lead me to believe the Chinese hammers weigh more than their markings indicate.

A mould maker knows a bullet alloy will shrink upon cooling. So, he knows the cavity he cuts must be larger (by some predictable amount) than the bullet the customer wants to cast.

The maker also knows that different alloys shrink varying amounts, so he usually has a list, or chart, or some other means of choosing the size he will make the cavity. Perhaps the chart was developed using pure math...maybe it came about through personal experimentation...or he might have obtained the data from the Chinese.

In any case, his moulds (and only his moulds) 'exhibit the same behavior', one that does not please you.
Is it possible that his cavities are cut to the wrong dimensions...perhaps because his chart is wrong?

If eliminating the logical still leaves a question, then it may be worth the trouble of an in-depth study of the metallurgly and chemistry involved.

Or not...

CM

[AriM]

OK, sounds good. You need not mention the mold maker.

Some people find that with their alloys and their pouring technique, molds made from very conductive alloys, such as aluminum or brass, pour best if the mold is heated pretty hot, and the melt kept hot likewise. If the dimensioning of the mold fits the alloy and technique, then all works out well.

However, sometimes the best results are obtained if the mold is kept quite hot, but the alloy is not heated super hot. Depending on situation, experience, and pouring technique, that balance of temperatures can be tough to maintain.

So, sometimes the easiest practice is to keep both mold and melt very hot. It is well known that the hotter the melt when pouring, the more shrinkage one can expect of the castings. It is easy to see that if the dimensioning does not match the alloy, the result may be a bullet that looks great, but is slightly under the desired as-cast dimensions.

The first relation we can make is more heat produces more expansion of the metal, and thus the hotter the pouring temp, the more shrinkage in the castings. This is one reason why it's standard foundry practice to only pour as hot as needed, but no hotter. That practice works well for pouring bullets.

The less alloy component in the lead, the more shrinkage in the castings. Pure metals almost always exhibit more shrinkage upon cooling than their alloys. So, the second relation we can make is that the more alloy component in the lead, the less shrinkage upon cooling.

A third relevant factor presents itself, and that is rate of cooling. A very conductive mold alloy has the potential to cool the castings very quickly. Some casters, used to iron molds but new to using Al mold blocks, have reported some initial difficulty with this difference. The rate of cooling affects the ability of the cooling metal within the mold cavity to draw more molten metal from the volume of molten metal in the sprue. If the casting within the cavity freezes or 'skins-over' quickly, the result can be that the cavity will be starved and the castings may fill-out perfectly but still drop under the desired dimension. Method of pouring, such as ladle vs forced bottom-pour, can affect rate of cooling.

I feel that these three underlined factors must each be considered in your situation, as they are observable, factual variables that can be altered to suit conditions or practice.

Good luck.

this is an excellent reply, and I thank you for it.....I think that i am actually running the melt TOO HOT. I run it at the same temp as my aluminum moulds. I do think that the excessive shrinkage, is due to overheating of the alloy. It is suggestive in your reply. It is an area that i have yet to adjust. I pre-heat the mould, and it fills out quite nice. I am going to try running the melt cooler, but keep the mould hot. This makes sense. Excellent suggestion. Thanks again.

I think i have made the assumption that hot mould should always be run with a hot melt. Bad on me....now comes the tricky part. Regulation of the mould temp. I wonder how I am going to keep it hot, yet keep the alloy cool. Looks like I have some things to try out, before I can point any fingers at a bad mould. This is exactly what i was fishing for....

Now on the issue of the original question....do you think antimony becomes fully solvent in the pot? This would go against what many books say, and what many casters seem to experience. Including my own experience. I have noticed that high antimony content alloy, seems to have large crystaline structures swimming around in it.

Maybe another issue of temperature?

[AriM]

AriM:

Well you see there is a way for a law to be changed and it is by the proof of a new one

The scientific method is based on:
Ask a Question
Do Background Research
Construct a Hypothesis
Test Your Hypothesis by Doing an Experiment
Analyze Your Data and Draw a Conclusion
Communicate Your Results

Some here are a bit fussy about things and feel that "this" or "that" is absolute. I am along the range that there could be change and many times there is change. It is all how a person words things that yield a better understanding and acceptance on this forum. Do not get me wrong here as this forum is the best wealth of knowledge for a cast bullet enthusiast.

I use for example a lot of:
probably
should
in my opinion
this is what I have discovered
this is what works for me
take it for what it's worth
I believe
among a variety of other neutral terms

The question you propose is good one which has many responses here on the forum and it is also another debate which ruffles feathers. Another classic is the debate over hard and soft bullets etc. I, like you, and many others here have had one constant to casting and reloading..............things are always the same and yet always changing.

I enjoy reading of people here who have initiative to stand outside the box and it is even more inviting to read of those who have practical knowledge of their actual real life data. You mentioned that when you proposed the thought of a different lube that you were shot down (no pun intended) and it was only when you had experiences and data collected with it that people opened up and took more interest once you posted your results.

Your lube experience mocks the scientist method and with it comes the understanding and acceptance of others.

I am not so sure it mocks the method...in fact i think it exemplifies it. I made a theory, based on experience and knowledge/logic. I used the scientific method to test and refine the lube. I Shared my findings. Is this mockery of the method?

The results are backed with data, observation....evaluation....testing and an end result.

[454PB]

My theory about heat treatment, is that it's just a surface treatment. If we were to dig into the core, we would find a softer alloy.

I believe the reason for this, is that the hotter portions of the melt bind in the center of the casting. The antimony and other materials find their way to the surface. This would explain surface heat treating also. Since lead does not respond to heat treatment. Therefore the metals that do respond to quenching are on the outside of the boolit, this is why only the outer layers of the boolit are harder. As you get into the core you find softer material.

Is this due to more rapid cooling of the outer layer, or metal oxidation? That is beyond my ability to test....

I can prove this wrong, and I've done the testing. Heat treatment hardens more than the surface.

I've never used a brass mould, but I recall the new learning curve when Lee began making aluminum moulds. For years before that, I had used nothing but steel moulds. My casting technique had to be changed to produce acceptable boolits. I assume the first use of a brass mould would be the same.

[RobS]

I am not so sure it mocks the method...in fact i think it exemplifies it. I made a theory, based on experience and knowledge/logic. I used the scientific method to test and refine the lube. I Shared my findings. Is this mockery of the method?

The results are backed with data, observation....evaluation....testing and an end result.

I didn't me mock in a sense of ridicule..........a ment a mockup

I will definately make that change............see..............I told you a simple slip in vocabulary usage and we have a totally different intent