Casting Temp effect on bullet diameter-- Thoughts ?

[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:



And since Diameter goes ∝ √weight
Just the raw data then . . . .
Thoughts ?

[Mike / Tx]

I did a similar profile several years ago with the Lee 452-300 casting for my 454. I found my actual best temp for those was between 680 - 720.

That said it also depends on the alloy and the mold. I've been using some of the MP brass molds and usually run the alloy up around 740, where the HG 4 and 6 cavity I have and depending on the alloy I run between 720 up to around 780 degrees. With my alloys this usually gives me the closest weights to what the molds are supposed to drop.

[ballardw]

Generally volume of almost anything expands as temperature increases with exceptions at phase state changes (example: water as it freezes initially expands, then contracts as temperatures drop).

Since molds 'measure' by volume, I am not surprised that hotter pours get slightly less weight after cooling. Any detectable diameter difference?

[mehavey]

...not surprised that hotter pours get slightly less weight after cooling.

actually, more weight (wel... 5th significant figure/statistically insignificant)

Any detectable diameter difference?

....since Diameter goes ∝ √weight -- None.

The real conundrum is that while the steel cavity does expand w/ heat, any advantage of the hotter lead in taht expanded hole is totally erased on cooling since hotter lead has 3x contraction compared to steel when the lead cools.

[AzShooter]

I did all my casting on my Waage at 720 degrees and the bullets were very consistent. Changing temp will change your weight and girth. The Waage holds it's temperature more consistently than any other pot I've tried.

[mehavey]

Changing temp will change your weight and girth.

But other than the 600° start group, it didn't.
That was not what I expected.

[Beagle333]

I almost always use 725°, but I almost always am casting brass HP molds.

If I'm casting my Lyman steel molds, some of them like to be cooler to get closer to the desired size. But if I run them hot and it drops a little smaller, I just PC them back up to size.

[big al hunter]

I have found that steel molds don't change the bullet diameter much with temperature gain. But my 6 cavity aluminum molds drop bullets that are impossible to size back down to the diameter the mold is supposed to drop. This only happens when the mold gets hot enough to drop "frosty" looking bullets. But it is consistent across 3 molds and 3 diameters/weights. I don't have a thermometer for my furnace yet. Might be my next purchase....

[FrankenMauser]

Did you measure the diameter?

I make use of temperature differential with a few molds, to save effort sizing or gain just a bit of diameter for larger bores.
Hot alloy + 'cold' mold = smaller diameter
'Cold' alloy + hot mold = larger diameter

[Shadow9mm]

I will have to take some measurements. I generally cast around 725. However I powder coat and when casting gas check bullets I generally cast around 800 as the gas checks go on over the PC easier. Hoping to cast again soon, gotta cast on my portch and it has been raining the last several days.