with a hotter mold cast smaller bullets?

[Shadow9mm]

I feel like an idiot for asking this question, I apologies in advance. When things are heated they generally expand. But in what direction? would the entire mold expand outward from the center? or would each half of the mold expand towards the bullet making it smaller? if so how much? are we talking 0.0005 or less than that?

[ryanmattes]

I'm not an expert.

But thinking about it logically, I don't think the mold expansion would be enough to notice. The lead temp, on the other hand, would have a much bigger impact. Cooling from liquid to solid is generally when the most obvious contraction occurs, so the hotter the lead, the more I would expect it to shrink as it cools. Likewise, the cooler the lead, the less shrinkage I would expect.

Anyway, that's my intuitive thought on the matter, but I could be completely wrong. Plenty of things don't make intuitive sense to me.

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[mehavey]

The hole in the mould expands within temp rise.
But hotter alloy shrinks more coming down from higher cast temps.

It's a race....

"In general"... I find cooler casting gains me a thousandth or so

[Winger Ed.]

I heard a vicious rumor that depending on what additives are in your alloy-
they will cause different amounts of shrinkage too.

In my experience, the sizer die seemed to iron out whatever difference that was between
what the boolits dropped at, and what I wanted to to be.

[JonB_in_Glencoe]

So, I have this one Lyman mold (410610).

When casting with a typical alloy like COWW at a typical temperature alloy (690º), and at a typical pace, where the boolits drop a dull grey, but not frosty, and have crisp sharp edges. Then boolits have a GC shank that's a wee bit large for the GC I want to install.

So, when I dial up the heat on the pot to about 720º and cast at a faster pace (so the mold gets hotter) making the boolits drop quite frosty, but are uniform. The edges are not as crisp and have rounded look to them, but again they are uniform. The boolits measure a wee bit smaller and the GCs snap on easily for a fit I consider perfect.

I surmise, Hotter means smaller.

An additional question, does antimony content play a role? well, I know boolits will age expand when there is larger amounts of antimony, but I do NOT know that they will cast smaller with lesser amounts of antimony...but maybe?

[Rcmaveric]

The alloy content will play a bigger role on bullet diameter than temperature. More specifically the amount of antimony. It would take a chemistry lesson to explain it.

Temperature would be very miniscule and not affect much. On the other hand you pour some pure lead in a mold design for a hard alloy and you might be so undersized you lead a barrel. I pours some wheel weight lead into a two part shot gun slug mold designed for pure lead and almost broke the mold getting it out. Thats how stuck the slug was on the center pin.



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[M-Tecs]

I feel like an idiot for asking this question, I apologies in advance. When things are heated they generally expand. But in what direction? would the entire mold expand outward from the center? or would each half of the mold expand towards the bullet making it smaller? if so how much? are we talking 0.0005 or less than that?

As atoms heat up the vibrate more and spacing increases. It's like a balloon expending. Every atom is moving away from every other atom. In 2D it's easy to see. Take a dozen dimes and a dozen quarters and make a circle. The quarters are the atoms vibrating in a larger area.

[high standard 40]

My experience only. I cast the with RCBS 7mm 145 Sil more than any of my other molds. This is a bore rider design. To make it fit my chamber properly I have to size not only the drive bands, but also the nose. Sizing the nose has led to me making the following observation. When the combination of melt temp and mold temp gets higher than this particular mold likes, I start to see an area on the bullet nose that appears to be very slightly frosted. When I size the nose of such a bullet, that frosted area will not be touched the nose sizing die, while the rest of the un-frosted nose will be sized. Obviously there is some shrinkage going on at that portion of the mold that is getting too hot. In my opinion this can cause an out of balance situation and adversely affect long range accuracy. By starting to use a PID and carefully controlling my timing, I can reduce this shrinkage to a very seldom occurrence. And weight sorting has shown much better consistency. So in my opinion, at least as it applies to my situation, higher heat can cause shrinkage of the bullet.

[JonB_in_Glencoe]

uneven and un-uniform boolit shrinkage can be caused by mold being too hot, but is also caused by other factors. While Dan's testing (in the link) doesn't mention it, I find that long skinny rifle boolits are most susceptible, but then I rarely cast Large Boolits like Dan's.

https://mountainmolds.com/shrunken-bullet-syndrome/

[gwpercle]

I feel like an idiot for asking this question, I apologies in advance. When things are heated they generally expand. But in what direction? would the entire mold expand outward from the center? or would each half of the mold expand towards the bullet making it smaller? if so how much? are we talking 0.0005 or less than that?

What , exactly , are you trying to do ... or is the question simply rhetorical ?
Gary

[414gates]

The expansion of the mould under normal casting temperature is irrelevant.

Cast bullets are sized to a very specific diameter after casting, the exact size of what the mould drops is neither here nor there.

The co-efficient of expansion applies to all metals. You can work out the dimensional expansion of any mould using basic math. For example, steel will expand at roughly one six millionth of an inch per degree farenheit. The expansion of your mould at 3 or 4 hundred degrees can't even be measured.

[mdi]

One of the Lyman manuals has a chart of various alloys used for bullets at different temps and resulting size and weight. Sorry, I don't have that manual in the house, it's in my shop library.

"What , exactly , are you trying to do ... or is the question simply rhetorical ?
Gary". Sometimes a feller jes wants to know...

[Green Frog]

The question has great relevance to those of us who cast their bullets to be shot unsized. I hav noticed that small differences in alloy or large variations in casting speed (giving swings in mound temp) give measurable differences in bullet weight and diameter. If you size a bullet to get a desired diameter, the weight can still be different from its siblings.

Froggie

[414gates]

The question has great relevance to those of us who cast their bullets to be shot unsized. I hav noticed that small differences in alloy or large variations in casting speed (giving swings in mound temp) give measurable differences in bullet weight and diameter. If you size a bullet to get a desired diameter, the weight can still be different from its siblings.

Froggie

Alloy composition changes bullet weight and affects bullet shrinkage, that is what I read read about in Casting 101.

The OP question is does the heat make the mould expand enough to affect the measurable cast bullet size, and the answer is no. Definitely not.

[mehavey]

The mould cavity does not expand one way of the other w/ temp
The alloy shrinkage coming out of that cavity, does. . .

[M-Tecs]

Thermal expansion is easily calculated. On an aluminum mold with a .500" cavity with the mold block temperature increase of 300 degrees the cavity will expand 0.001845" for a total of 0.501845".

[mehavey]

The mould block may expand slightly, but the cavity will not 'effectively' expand over that of a lower temp

https://www.youtube.com/watch?v=UBwO7hXORAI

[M-Tecs]

The mould block may expand slightly, but the cavity will not 'effectively' expand over that of a lower temp

https://www.youtube.com/watch?v=UBwO7hXORAI

You may want to watch that again starting at 1:30.

The hole diameter in any geometry will expand. Think about what is happening on the atomic scale. As atoms heat up they vibrate more and spacing increases. It's like a balloon expanding. Every atom is moving away from every other atom. The vibratory action increases with heat so the RMS distance of the individual molecules increases therefore the hole will expand.

In 2D it's easy to see. Take a dozen dimes and a dozen quarters and make a circle. The quarters are the heated atoms vibrating in a larger area. The hole in the center of the quarters is larger than the hole in center of the dimes.

Area expansion is basically the same as a photographic enlargement as shown here:
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thexp2.html

https://www.webassign.net/question_assets/buelemphys1/chapter13/section13dash2.pdf

Great visual here but in heat fitting one part is heated and the other part normally is cooled or left ambient temperature. I think he is doing it that way to illustrate that different materials have a different expansion rate. In this example he is heating both parts like we are doing in casting but the lead is normally almost double the temp of the mold block and lead has a greater coefficient of expansion than any of the three commonly used block material.


https://www.youtube.com/watch?v=X-oVB4mLcAA

[T Gray]

One time years ago I attached a thermocouple to the two cavity mold. I monitored the mold temp. as I was casting. I weighed each bullet as I was casting and as the mold got hotter, the bullets got heavier. Nothing else changed but the mold temp. I don't remember is I measured the bullets for diameter but they were definitely heavier in proportion to the temp. increase. Can't say if they were larger or denser

[Shadow9mm]

What , exactly , are you trying to do ... or is the question simply rhetorical ?
Gary

I have 2 goals, I want to make sure my gas checks go on easily, hopefully over powder coating, and understand how my molds work so I can properly regulate their temperature to get the desired results. I understand the lead temperature components, but not the mold side of things.

[M-Tecs]

A practical application of thermal expansion.


https://www.youtube.com/watch?v=j_sgiTa3gew

[bangerjim]

A sizing die of the correct diameter for my barrels solves all the problems for me

[mehavey]

https://i.postimg.cc/4ddv743f/Mould-temp-effect.jpg

[blackthorn]

If I am reading it correctly, the information set out in post #23 is dealing with a one piece steel cylinder. A mould is not a one piece cylinder it is two pieces of metal (half-blocks) held together with hand pressure. Whole different ball game when it comes to expansion. I seem to recall this subject having been dealt with a long time ago on this forum (but it may have been somewhere else). Memory is dim, so----

[M-Tecs]

If I am reading it correctly, the information set out in post #23 is dealing with a one piece steel cylinder. A mould is not a one piece cylinder it is two pieces of metal (half-blocks) held together with hand pressure. Whole different ball game when it comes to expansion. I seem to recall this subject having been dealt with a long time ago on this forum (but it may have been somewhere else). Memory is dim, so----

Yes it was at least three previous times. Expansion is expansion. One or two pieces it makes no difference on how the ID of the mold expands.


https://i.postimg.cc/4ddv743f/Mould-temp-effect.jpg

The chart in #23 is full of errors. The mold block temp is low (200 degrees) and they are way off on the contracted bullet size. I didn't run the numbers to find their math errors but I do know 0.452 molds do not drop 0.441 or 0.443 bullets.

[mehavey]

Where did a 200° mould come from?
That was the Delta-T, change in temp

Read the chart again... (Mould Temp is admittedly simplified to lead temp for sake of example)

The lead/mould starts at To (700°) and an internal diameter of 0.4520000"
The rise in temp (delta T) is 200° to Th = 900°
The internal mould diameter has now expanded to 0.4528498"

Lead cast at 900° comes out initially at (gasp) mould diameter -- 0.4528498"
But it then cools down 832° to room temp (68°) and a much smaller 0.4419234"

So before you say "full of errors..." and that you don't have time -- please RTP (read the problem)
Make your own temp start/rise/stop assumptions/do your own math for alternate answers --
realizing that lead contracts three times faster than steel with temp
(... otherwise you could never get the bullet out of the mould to start with.)

[M-Tecs]

Where the heck did you come up with a 200 degree mould?

Read the chart again
The mould starts at To (700 degr) and an internal diameter of .4520000"
The rise in temp (delta T) is 200 degrees: to Th = 900 degrees
The internal mould diameter has now expanded to 0.4528498"

Lead cast at 900 degrees comes out at (gasp) 0.4527498" -- mouilsd diameter
But it then cools at room temp (68 degrees) to much smaller 4419234"

So before you simply say "full of errors..." and that you don't have time -- please RTP (read the problem)
-- and do your own math for alternate answers

Look at the first chart. The Delta T is 200 degrees which expands the .452 cavity to 0.4528498. Most molds cast best around 400 degrees and yes I have a thermal couple on some of my molds. A 900 degree mold is fantasy land.

As to the mold using .452 size is also incorrect. That would be the finished drop size. The mold maker will have it oversize to allow for the alloy shrinkage so yes that chart is full of errors. The chart roughly indicates 2.5% shrinkage. More realistic is 0.5% to .0.7%. It's not that I don't have time to run the numbers it's that the chart is so full of garbage that the only way to fix it is to throw it away and start fresh.

At some point common sense needs to take over. Anyone that has lapped a mold or leaves bullets in the mold know you don't have .011" shrinkage on a .452 mold. That would rattle when you shake it. Casting with a 900 degree mold on what planet???????

https://castboolits.gunloads.com/showthread.php?85580-bullet-shrinkage-allowance#:~:text=It%20all%20depends%20on%20the%20 gun%20barrel%20and,cut%20the%20mold%20to.360-.361%20this%20allows.001-.0015%20alloy%20shrinkage.

https://castboolits.gunloads.com/showthread.php?336108-Lead-Shrinkage-Data

[mehavey]

I told you up front the simplified assumptions to test the boundary values.

So make your own assumptions.
Do your own math. (the equations are the same)
Come up with your own answers

But you can't escape the fact that whatever diameter gain in the steel you get,
it's wiped out (and then some) by 3x contraction when the lead cools.

[M-Tecs]

I told you up front the simplified assumptions

So make your own assumptions.
Do your own math.
Come up with your own answers

But you can't escape the fact that whatever diameter gain in steel you get,
it's wiped out (and then some) by 3x contraction when the lead cools.

First you claimed the mold ID did not expand with temperature. That was not correct.

Second, not a single poster claimed that lead, aluminum, brass or steel had the same coefficient of expansion. Not sure where you are getting that. Maybe the same place as the 900 degree mold.

Third, this is not assumptions it's physics and it is 100% repeatable.

below is a post from Tom of Accurate Molds. He is a true expert in bullet mold making. He recommends cutting a target goal .610" at .6135" to allow for shrinkage.

https://castboolits.gunloads.com/showthread.php?429387-Sizing-a-custom-bullet-mold&p=5240745#post5240745

[mehavey]

So ... use your own thermodynamics, with your own assumptions, via your own math
Remember the question: Does higher-temp (lead/casting) produce larger -- or smaller-- diameter bullets once cooled?

I'm willing to change my mind.



postscript: See LASC reference: http://www.lasc.us/CastBulletNotes.htm
>
> Tip: The size and weight of bullets of a given alloy will vary according to
> casting temperature. Higher temperatures will result in greater shrinkage
> as the bullet cools and produce a slightly smaller and lighter bullet than
> one cast of the same alloy at a lower temperature.
>
(I knew I'd seen it somewhere)

[M-Tecs]

So ... use your own thermodynamics, with your own assumptions, via your own math
Remember the question: Does higher-temp (lead/casting) produce larger -- or smaller-- diameter bullets once cooled?

I'm willing to change my mind.

How about trying to answer the OP's question????????


I feel like an idiot for asking this question, I apologies in advance. When things are heated they generally expand. But in what direction? would the entire mold expand outward from the center? or would each half of the mold expand towards the bullet making it smaller? if so how much? are we talking 0.0005 or less than that?

To answer your question hotter mold blocks produce larger bullets. The hotter the alloy the smaller the bullets. That has been common basic casting knowledge for a very long time and it was not part of the OP's question.

[mehavey]

To answer your question hotter mold blocks produce larger bullets.
The hotter the alloy the smaller the bullets.
Since one drives the other...

Hotter/Faster means smaller/lighter.
Cooler/Slower means larger/heavier.

Can we agree on that?

[mehavey]

Tonight I went out to the garage for a TempTest-Run

Waage 20# Casting Pot (K-4757)
Lyman #2 (Rotometal)
Standard Lyman Contact Dipper Pour (for me)
Accurate 45-200H (H&G-68) 200gr 45 ACP Dbl-Cavity Mould
Lyman Lead Thermometer
Hot-Plate Mould Preheat during Lead Pot Heat
My standard #2 Lead casting temp is set 720°
All the below occurred as Temp rose to, and past, liquidus/600°

At 600° degrees/all-liquid I stirred in -- repeatedly top to bottom/bottom-to-top -- very large pea-sized piece of 50-50 bullet lube to Flux/Clean
Restabilized at 600° and I began to cast -- steady rate of 5 casts (10 bullets) every two minutes.
First cast keeper and all grouped in growing sets of 10 as the Temp rose to standard 720° for last minute of casting
Quit and allowed all to cool to room temp.
Weighed each group of ten as a group, and divided-by-10:

https://i.postimg.cc/50ZLcrVL/Cast-Weight-vs-Temp.jpg

Just the raw data then . . . .