Aluminum vs Iron Molds, temp question

[Jim Flinchbaugh]

I've just started casting on my own recently, after being indoctrinated by and older veteran caster from my rifle range. While learning from him, we used iron Lyman molds, casting 311's for my 7.65x53 Argentine.
My first batch on my own was casting .430" 240 grainers from aluminum LBT molds.
The first run, the slugs had a grainy look to them & not shiny. After some fiddling about, I tried slowing my pace, allowing the mold to be cooler than the first try. These came out much better looking, more weight consistent, and better filled out around the grooves.

My question is, is it normal for an aluminum mold to want to be cooler than iron? I assume because it heats up and cools down faster, that your pace has to be a lot more on the money to get consistent results?
I found by slowing the pace, and allowing a few minutes to cool every 20 or so rounds that I got better results.
Normal or am I goofy:veryconfu

On edit:
This was straight wheel weights, Coleman stove, Lyman pot and homemade dipper
(thermometer on order from SwedeNelson :D

[Dale53]

Jim;
You with learn that bullet casting is part scientific and part art. There is no "one size fits all" when it comes to bullet moulds. Some like a bit less heat and some like more.

I kind of tailor my heat to what the mould is telling me at that specific moment. There are many variables in bullet metal (every mix of alloy is a bit different than any other mix). However, as you do a bit more bullet casting it kind of comes together. For me, it has become a very pleasurable way to spend time. I actually ENJOY bullet casting. I guess I like turning out all of those VERY attractive bits of frozen metal that we call "Boolits"...

As a start, I normally cast between 700-750 degrees (by a thermometer). My "normal" alloy is WW's+2% tin. I use a bottom pour pot exclusively (I have a couple of RCBS electric pots) and tend to use multi-cavity moulds by preference. I have a manicurists fan that speeds up the sprue hardening process (takes from 2-3 seconds to be ready for cutting the sprues). The fan also maintains proper mould temperature and has a "by product" of cooling the pile of bullets. Just a few minutes after the pot is empty, my 20+ lbs of finished bullets can be shoveled gently into a box to move from my utility barn to my basement shop for lubing, sizing, and boxing.

I ALWAYS pre-heat my moulds, whether brass, iron, or aluminum on a hotplate set to bring my mould up to about 400 degrees. I am casting great bullets in one or two casts. No delay waiting for the mould to heat and no breaking Lee six cavity handles because my sprues are too cold (providing heavy resistance when trying to cut six cold sprues at once).

YMMV
Dale53

[JIMinPHX]

In general, I need to run my aluminum molds hotter than my iron molds.

In general, I need to run smaller diameter & longer length boolits at higher temperatures.

In general, I need to run higher temperatures when using alloys that are closer to being pure lead.

Frosty looking boolits often mean that you are at or near the maxim temperature that you want to use. Frosty is not a bad thing though.

Shiny boolits usually mean that you are running a little cool.

If fill out is poor, you also want to make sure that your mold is clean. Any left over lubricant or other contamination in the cavity is a bad thing. You do want high temp lube on your pins & sprue plate though. Bullplate is the local favorite with the board members here.

As was already said, there are no hard & fast rules (aside from the lube). Each mold is a unique beast unto itself. My advice is to try a few different things & see what happens.

[quilbilly]

I absolutely agree with Jiminphx. My aluminum molds do like it hotter. My pace is that as soon as the metal frosts on top of the sprue, it gets cut and the boolit drops. One thing I have found with my aluminum molds is that they pour better boolits more quickly if I "smoke" a new mold as soon as it gets hot the first time. From then on I get good pours after only 4-6 rejects. That may change if I start pouring boolits smaller than 7mm though but time will tell.
If you don't know the term "smoking a mold", it is just holding a lighter or match to the cavity to get a little carbon (just a little!!) coating on the inside. Care should be taken to do this only on a hot mold to boil off the moisture in the carbon or you will be a victim of an unhappy surprise (steam blowing molten lead out to the sprue for several feet.

[peerlesscowboy]

I pretty much agree with JIMinPHX too. I suspect what caused the OP's frosted bullets was the 240 grain .44 bullets are bigger diameter and heavier than the .311 bullets he'd cast previously. Assuming approximately same size mould blox, the more molten alloy you pour into the mould the hotter the mould will run if you don't slow the cadence.

John C. Saubak

[Jim Flinchbaugh]

Thank you for the replies! I know there is still a long learning curve for me, and I am quite good at figuring things out by what it is telling me, if I know what to look for :)

The LBT molds I have are 2 cavity, and they where preheated and smoked before beginning casting. I had no trouble dropping boolits.
The first few pours didn't look great, then as the mold came up to temp, they got nice, then started to get the grainy look. After slowing my cadence, I made a string of nice slugs that I was happy with. Weights only varied 3-4 grains after I got what I thought was good looking pours, 234-238 grains, in a 240 grain mold, without any alloy modification to the smelted wheel weights. I need to locate some tin!

[Bret4207]

Listen to the mould. Overall aluminum needs a bit more mould heat (cast faster) than iron, but individual moulds vary greatly in what they want on a particular day. Gotta be flexible. Light frosting usually gets me near perfect fillout- and I'm real picky about what I call "near perfect". But some moulds don't seem to like to work at the frosty level, others sort of demand it. But, change the alloy and that will change what they want. Like Dale said, that's the art part.

It sounds to me like you have a pretty good handle on things. You were willing to play with things to get good boolits. Sounds good to me.

[epj]

My 6 hole Lee molds seem to like to be real near 800* to cast well.