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...mo/thexp2.html

https://www.webassign.net/question_a...ion13dash2.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.

[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.