Heat loss in brass vs iron molds

[jamesp81]

I haven’t done any casting in a while, mostly because it was a complete disaster the last time I tried. The issue I encountered was that I could never go fast enough with aluminum molds I have been using. They lose heat extremely rapidly and I’m new to this, so going fast isn’t something I’m really up to. Yet.

I want to give this another attempt and have read that brass loses heat slower than aluminum and iron loses it slower even than brass. I’m trying to decide between the two but having trouble gauging the differences.

I am not interested in a fast cadence. Ask it this way, is brass closer to iron in terms of heat loss or closer to aluminum? Is it more similar to iron’s slower pace or aluminum’s faster pace?

[M-Tecs]

Brass holds heat more that iron. They all have their advantages and disadvantages. Steel is the most durable except for rust issues. Quality aluminum molds work very well for me. I like them all but prefer brass. Brass has tinning issues and is relatively easily damaged.

http://accuratemolds.com/FAQ.php
What are some of the properties of the different mold metals?

2024 Aluminum is very durable, light weight, and inexpensive. Its propensity to change temperature quickly is seen by some as a disadvantage, since molds produce their best bullets within a narrow temperature sweet spot.

Ductile Iron is the most durable of the commonly used mold metals. It is easier to maintain a more consistent temperature. It is lighter weight than brass and heavier than aluminum. Its biggest disadvantage is propensity to rust. Iron is rough on delicate boring tools, and so it is the most expensive.

360 Brass is a bit heavier than iron, and costs less because of ease of machining. It maintains temperature very well. Some see its weight as a disadvantage.

Sprue plates and hardware are carbon steel.

My favorite for my own casting is aluminum.

[nhyrum]

Brass holds way more heat.

I've found with aluminum molds, when I started, turning up the pot temperature helped keep the mold hot

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[kungfustyle]

Get a hot plate or camp stove and keep your mold on it to get it back to temp. Don't use the aluminum mold when it's under 50, if you are casting in a garage or outside.

[243winxb]

Jamesp81,

The size of the mold may have something to do with heat retention. The Lee 2 cavity heats up fast and gets to hot, compared to Lyman (in middle) & other iron molds.

You should learn using a Lee 2 cavity? The 6 cavity may loose heat to fast? I never used a 6 hole.

Preheating Lee molds, temperature must be under 400F degrees. See Lee Website. https://support.leeprecision.net/en/knowledgebase/article/alignment-pins-fall-out-overheating-double-cavity-mold
The aluminum molds will not overheat by simply casting but can be overheated by preheating with a hot plate, torch, setting on top of the pot to heat up or immersing in molten alloy for an excessive amount of time.
Best to heat mold by casting & pot at maximum temperature.
https://www.thehighroad.org/index.php?media/size-of-molds.4159/full

[VariableRecall]

The size of the mold may have something to do with heat retention. The Lee 2 cavity heats up fast and gets to hot, compared to Lyman (in middle) & other iron molds.

You should learn using a Lee 2 cavity? The 6 cavity may loose heat to fast? I never used a 6 hole.

Preheating Lee molds, temperature must be under 400F degrees. See Lee Website. https://support.leeprecision.net/en/knowledgebase/article/alignment-pins-fall-out-overheating-double-cavity-mold
Best to heat mold by casting & pot at maximum temperature.
https://www.thehighroad.org/index.php?media/size-of-molds.4159/full

I've personally used two of Lee's selection of 6 cavity molds, the 148gn Soup Cans (.38 Spl Wadcutters), and 124gn Round Nose 9mm. While it is a little tricky to get everything warmed up properly, and not too warm! I've had that issue before. The sheer volume boost you can achieve with 6 cavities is well worth the babying to ensure all 6 cavities are dropping boolits properly. You will get about 3-5 runs that aren't optimal since all the cavities have to get up to temperature, and you personally have to get into the rhythm of moving the mold so far backwards and forwards.

Much like any post-casting session lookover, you really need to make sure that all the bullets you cast have been properly filled out. My favorite way to do that is to find a "perfect" boolit and use it for comparison to other ones. Tiny flaws such as not as filled out driving bands, shallower bases, or broken driving bands can be tricky to spot without a reference.

[gwpercle]

Custom Moulds are generally more massive than Lee .
A NOE 4 cavity aluminum is about as heavy a mould as my 70 year old hands and arms can handle .
I have no problem with the NOE 4-aluminum loosing heat with a normal cadence ...I don't move that fast any more either ... Brass moulds are even heavier, I wouldn't be able to cast but maybe an hour before my hands tire ... In fact my last 3 NOE moulds have been 3 cavity Aluminum ...to lighten the weight ... NOE makes their moulds from much larger blocks of aluminum than Lee does .

Steel moulds also hold heat well and aren't as heavy as brass and are nice to work with .
Gary

[nhyrum]

Are you using a bottom pour or filling them with a ladle? If you're using a ladle, I'd turn the pot up a bit, since it takes the lead longer to get from the pot into the mold. For bottom pours, turning it up a bit will stop help, but I've found, at least how the Lee pots work, that if you open the spout enough to fill the cavity in about a second or less is about what it takes, being careful to not let the lead flow or splash into the other cavities.

I generally like having everything hot enough I have to wait a second or two for the lead on the sprue to solidify, then I'll turn the pot down significantly(I'll start with my Lee pot on 9 or 10 then end up turning it down to about 5-6 once everything gets warm. You don't have to particularly move fast, but the cavities do like to be filled quickly.

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[centershot]

I haven’t done any casting in a while, mostly because it was a complete disaster the last time I tried. The issue I encountered was that I could never go fast enough with aluminum molds I have been using. They lose heat extremely rapidly and I’m new to this, so going fast isn’t something I’m really up to. Yet.

I want to give this another attempt and have read that brass loses heat slower than aluminum and iron loses it slower even than brass. I’m trying to decide between the two but having trouble gauging the differences.

I am not interested in a fast cadence. Ask it this way, is brass closer to iron in terms of heat loss or closer to aluminum? Is it more similar to iron’s slower pace or aluminum’s faster pace?

Are your bullets wrinkled in appearance? If so, then you are correct in your belief that the mould is too cool. With one exception all of my moulds are aluminum and I'm not having this problem, nor are most of us. So, a few questions please:

What is your alloy?

How do you pre-heat your mould?

Bottom pour or ladle casting?

Thermostat, PID, or none of these?

Let's see what we can do to help!

[country gent]

I really like my brass moulds as it seems like I cant mess up with them, I also use iron moulds with great results. My moulds are for large for caliber bullets. 360 grn 38s to 550 grn 45s. The size of the bullet also has a affect on maintaining mould temp, one reason 22 cal and 243 are harder to cast, way more block than bullet.

[243winxb]

Maybe this will help. https://www.thehighroad.org/index.php?media/casting-with-lee-molds.4127/full

[fredj338]

You have to be casting really slow to have enough heat loss with alum imo. In fact, I have to slow down to keep the alum cool enough so I am not waiting 30sec for the spru. I do prefer iron molds in general but over 4cav, they get heavy for longer sessions. Brass, I have one & never will buy another. Just too heavy. Quality alum molds like NOE & Accurate are a joy to work with in 4-5cavs. If you get a good Lee 6cav, they also work quite nicely.

[Stopsign32v]

NOE aluminum mold is the best mold I've personally ever used. Lightweight, big large plate to knock, and just flat out makes good boolits. There is nothing wrong with the brass ones except it takes a lot more effort to get them hot and making boolits.

Everyone on here was pumping the brass molds like they were the bee's knees but honestly I'll probably only ever get aluminum molds going forward from the custom mold makers.

[BMW Rider]

Here are some data on the subject from some of our favorite materials.

"Thermal conductivity: materials with low thermal conductivities are excellent at insulating, while high thermal conductivity materials are ideal for applications where heat needs to be moved quickly and efficiently from one area to another."

Thermal conductivity coefficients (W m −1 K −1) at 20°C and 1 bar (Source: Mechanical Engineer's Data Handbook, J. Carvill, 1994)
Aluminium 239
Brass (60/40) 96
Steel: mild 50
Iron, cast 55
Copper 386
Lead 35
Tin 67
Antimony 18

[popper]

I could never go fast enough with aluminum molds
I guess that your problem was the Al mould was not hot enough to begin with. Sprue plate needs to be hot enough so you can cut the sprue. Mould needs to be hot enough to not get wrinkles. Get a hot plate and use it. Lots cheaper than the brass mould.

[Stopsign32v]

I do not use a hot plate with LEE molds, I find it makes the molds and lead too hot and I end up with bad boolits. My pot gets set to 7 and I use the lead to heat the mold to the temperature it needs to be at. I pour into the cavities and keep pouring until the scoop is empty. Do that a few times and its good to go. Then I switch over to just pouring and leaving a nice puddle on top, shake it back and forth as it cools, and then knock the plate about 3 seconds after it solidifies to a dull color.

Makes picture perfect boolits.

[popper]

I find it makes the molds and lead too hot (hot plate?) Nope. I use a PID to control alloy temp, 725F. Wore the 40 cal Lee mould out from too much use - ole one with funky pins that are bad, mould still drops good bullets. Wait for the white/grey color change and open with gloved finger. I changed the plate tab to toward the handle, index finger opens it easy. Close the mold with sprue down, rotate and close the sprue.

[thompsonm1a1]

I use lyman steel all the time and have no problems, once the mold gets up to temp you are good to go. as soon as it cools off I use engine oil on it and put them back into the snap box I have never seen any rust on my molds. all my molds are like new condition.

[oldhenry]

There are other factors beside brass vs steel vs aluminum.
Refer back to #5 by 243winxb's photo. The 4 hole steel SAECO will heat up faster than the 4 hole Lyman. The Lyman is bigger. I have both and sometimes when casting both at the same time the SAECO has to "rest" & cool off every now & then. Also a steel/brass/alum mold casting heavy .45 cal. boolits will heat up faster than the same brand & same material casting 100 gr. 9mm or.380 boolits.

I use molds in all three materials & like them all. My favorite is brass.

[jamesp81]

Are your bullets wrinkled in appearance? If so, then you are correct in your belief that the mould is too cool. With one exception all of my moulds are aluminum and I'm not having this problem, nor are most of us. So, a few questions please:

What is your alloy?

How do you pre-heat your mould?

Bottom pour or ladle casting?

Thermostat, PID, or none of these?

Let's see what we can do to help!

Bullets are sometimes wrinkled or have what I would describe as cracks.

I preheat by dipping the corner in the melt for a short time. I finish heating by simply casting, understanding I’ll throw out the first few. I tend to find that I when I start throwing what looks like good billets, I sometimes do get too cool.

I ladle cast with my own redneck engineered ladle. The Lyman ladle just wasn’t big enough. I bought a cheap, $5 stainless steel soup ladle and drilled a hole in the bottom of it. It works well enough.

The alloy I think I need to throw out. It was WW to start with but I think when I fluxed it I ended up scooping out a lot of the tin. It’s soft enough you can slightly score it with a fingernail if you put some effort into it. While it’s likely a lot of my consistent leading problems are due to to this, I doubt they all are. Soft alloy sized 0.0015” - 0.002” over bore size in 45 ACP lubed with 45/45/10 really should not lead. But it does. Severely. I have no leading with the excessively hard hard cast commercial bullets you can buy, which leads me to believe that the advice on using no more than 10 or so BHN hardness for 45 is bad advice, at least where my particular pistol is concerned.

I tend to inspect a few bullets every other pour or so which might explain the cadence issues.



My pot is a Lee pot. No PID, thermostat, or thermometer.

[Petander]

I tend to inspect a few bullets every other pour or so which might explain the cadence issues.




It's better to keep casting without interruptions.

I was using two (small) Lee 476 molds the other day, first they were on a (recommended) hot plate and after a few pours I was able to alternate them with no downtime at all.

Fill mold #1, put it aside, fill mold #2, put it aside, cut sprue #1, drop bullets #1, fill #1, put it aside, cut sprue #2 etc etc. No need for hot plate during casting. A cool shed temp maybe 50 F.

I prefer brass because I can use three molds alternating like that.

But the OP needs to get his mold temp up. Is the mold clean? Keep casting! (I just got a Svarog alu mold broken in, I thought it was faulty but no, it just needed half a dozen casting sessions to make good slugs. )

[kevin c]

Nearly all my molds are multi cavity aluminum versions, and I do find them finicky temperature wise. I have to speed up a lot if it's colder or windy where I cast (outdoors); I can't inspect and cull each drop like I can when its warmer and windless.

With the semi wad cutter with a deep lube groove I'm casting right now, I have to speed up AND raise the pot temp (PID) 20° AND raise the preheat temp of the mold by 30° (K type probe in a cavity, mold on a hot plate), compared to NLG or shallow lube groove versions of same weight boolits dropped from molds from the same maker and same number of cavities. Even then, a little too slow and I get rounded or wrinkled bands; a little too fast and the sprue crumbles.

So I can confirm that the optimal temp range for an 8 cavity aluminum mold is narrow and hard to maintain in cold casting conditions. Since I need the boolits now, my workaround in this weather (can't cast indoors) is to cast in batches until I lose the light matte frost that I see in the best boolits, then reheat the mold on the hot plate while I inspect and cull the batch. An alternative might be to run hot and cool the sprue using the wet sponge method, though I hate having to break down the mold to oil the steel parts at the end of each session.

[nhyrum]

It's better to keep casting without interruptions.

This. I'll peek at the bullets as they pop out, but I do all my culling at the end, or if the mold starts getting too hot and needs to cool down. Leave the inspection until the end and turning the pot up, at least until you get into a rhythm could help getting up to temp at your cadence.

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[Char-Gar]

I have never had any problems with aluminum molds. They heat up faster and only after one or two casts are ready to go. I never have culled or even looks at the cast bullet until the casting session is over. I then cull and drop the culls and sprus back into the still hot pot. Lee aluminum molds are made from poor quality metal and the six cavity are the only ones of that make I will try to us. I started using NEI molds about 1980. I have found NOE and Accurate molds to be also of high quality.

I use a several tricks developed long ago by members of this board, they are:

I cover the top of the melt with about 1/2 inch of clay kitty litter. This makes fluxing unnecessary after the initial flux.

I place cold ingots on top of the pot lip to prewarm and put them in the pot as needed to keep a proper level. The pot does not lose much, if any temp this way. Yes, I use a bottom pour pot.

I put a shallow metal dish next to the casting pot with a folded cloth in it and water in the bottom. The water will wick up to the top of the cloth and keep it damp. When the cast is done, I turn the mold upside down and touch the spru to the damp cloth, which will cool it instantly. I then cut the spru, dump the bullet on a soft surface and do it again. Bruce B was the guy who came up with the notion of damp cooling the spru.