Aluminum Mold: Does it require a different technique?

[RG1911]

After a 7-year hiatus from casting, I'm starting again with a custom Accurate 2-cavity aluminum mold. Using my approximation of Lyman #2 alloy, it's casting a 324-gr boolit measuring 0.463" for my Marlin 1895 with the oversized Micro-groove bore (0.4595"). The boolit will be sized to 0.462".

Pot temperature is 720 degrees F.

Before starting I used a Q-tip and brake cleaner to clean the cavities.

After 30 or so throws, the boolits finally came out without wrinkles but are frosted (see image).

The question then is: Do aluminum molds require higher temps/faster casting/etc? I did not see an answer based on my search of the forum.



Thank you, Richard

[Wheelguns 1961]

The only thing that I can tell you is, you will need to play around to see what it likes. Large bullets in a small mold will quickly heat up the mold. You may need to keep them in the mold longer. You also may need to take more time between pours. I think this is the reason for the frosting.

[Sam Sackett]

Aluminum molds lose heat faster than iron molds. So, this means your casting cadence needs to be a little faster. Another thing to watch is the temp of the steel sprue plate. This will not heat up as fast as the aluminum mold. The hot lead can be cooled passing through the sprue hole, acting just like your mold is not up to temp. Once the sprue plate gets to temp, wrinkles go away and your mold will settle in and start producing good bullets.

Heating the mold on a hot plate with the sprue plate down against the hot plate is the best way to preheat that I have found so far.

Hope this helps!
Sam Sackett

[243winxb]

My thoughts on auminum. Frosted bullets not good. Mold to hot.

[Saxon]

in my short experience with a 2 and a 6 cavity mold on 45 acp
i heat it over the pot until the lead is ready to pour, and they come out clean and shiny no wrinkles.
when they start frosting i take a few extra counts and they come out non frosty again , so i am assuming it is getting to hot,
so i start slowing the count till they all come out on average shiny ish

[oconeedan]

Once I start making bullets, I cut the temp down (no digital thermometer for me) a little at a time. If the bullet is frosty, it is getting too hot. No amount of time in the mould will correct that. Simply turn the temp down.

[huntinlever]

Sorry for the hijack OP, but you've triggered some similar questions, thanks.

After coming to this thread I did some digging, because I've always sought what I knew anyway as a "frosted" surface. Unclear how to tell the difference between a "good" frosted and "excess" frosted but after doing some research here:

https://castboolits.gunloads.com/sho...l=1#post579030
https://castboolits.gunloads.com/sho...l=1#post579030

I did note the comment re finning, which happens with me from time to time and I don't recall it as a "thing" from past practice. The problem is I don't know metallurgy, so figured the sprue plate is getting too loose or something like that. I also read about the fact the alloy gets hotter as the pot empties out, which helps explain some things. I should measure the temp more often.

I take 94-3-3 to 725, and heat the Accurate Mold (2-cavity aluminum, 46-405 VG) on a hot plate prior to 1st cast, or when I'm breaking the rhythm for one reason or another. Typically my first stretch of casts the puddle solidifies in about 5-10 seconds and I take it to 12-15 seconds before breaking the sprue and dumping. As the session goes on - it occurs to me now, this is obviously as the alloy heats up with the pot emptying out - the puddle take longer to solidify and I will take up to 30 seconds between casts. That now signals the flaw of excessive temp, to me.

I should also mention that most bullets I cast take on a "frosted" appearance as they cool, but then as you can see (1st 4 L-R), they tend to become less so after heating then quenching.




The bullet at right was culled, and it is what I would call "excessively" frosted though again, I'm sure I'm lacking understanding of concepts and terms. You might also see the small finning, though rightly or wrongly, if it's only mild finning and I can "scratch" the finning and pull it clean, and the bullet weighs within specs, I'll keep the bullet. I accept bullets weighing 392.0-393.9, and any obvious visual defects are culled. Not sure if any bullet with any finning should be culled regardless (whether I can "fix" it or not).

[Bazoo]

I find that aluminum moulds need to be run a bit hotter than iron because they drop below optimum temperature quickly, not specially because they are aluminum. I get the best results if I'm just below frost temperature. Anytime I get spot frosting I back off though, because spot frosted areas are a bit smaller than normal. This makes the bullet out of balance.

[gwpercle]

Don't forget ... not a thing wrong with a nice overall frosty finish on a boolit ...
The frosty finish holds on to "coatings" very well and even help with tumble lube.

I strive to cast my boolits right at a "just frosty" temperature .
You will have to experiment with dial setting ... lots of variables will be in play so you can't say a number like 725 F is what is proper... I start out with the pot set on the hotter side and as the boolits start dropping frosty ... lower the temperature .
Casting over 50 years and I don't even own a thermometer... when they look right , that's the correct setting !
Gary

[Gobeyond]

I think it’s too cold when frost, because always fighting with quick drop in temp with aluminum. Especially those thin lee molds.

I get frost with lee. It’s ok. Not so much with others. Too hot and too cool are so alike, but more heat usually works. I have over heated a mold. It had nothing to do with frosted bullets. There must be all of 100 degree difference between the two.

[deces]

In my practice, frosted boolits have always been a result of the pot being too hot. Wrinkles are from oil or contamination in the mold or temp being low.

[RG1911]

This image, viewing from right to left, shows the progression of my cast boolits from super wrinkly, to beginning frost with very small wrinkles (outlined in red), to frosted with no wrinkles. Then, as the mold heats further, the frosting becomes more and more evident. I let the mold cool down before the frosting becomes excessive. (My alloy temperature is 720 degrees F.)



After about 50 throws, I went through the boolits making sure to pull out any that showed wrinkles, bad spots, etc. This left me with about 55 that looked good enough to use in tests to determine a good load.

I was almost to the size-and-lube stage when I decided to weigh the good boolits. This image shows the distribution:



There is a 4.4-grain difference between the lightest and the heaviest. I am uncertain how much that would affect a 45-70 at 100 yards. To be on the conservative side, I looked towards the center of the spread and found 40 boolits that had only a 1-grain difference between lightest and heaviest.

Thank you all for the great information and suggestions.

Cheers, Richard

[rintinglen]

In my practice, frosted boolits have always been a result of the pot being too hot. Wrinkles are from oil or contamination in the mold or temp being low.

^^^THIS!!! Hot frosts; cold wrinkles.
Minor frosting is no bad thing, provided it is even, and that is what I strive for, since I generally tumble lube or powder coat my boolits. However, extreme frosting or uneven frosting result in light, under-sized boolits and are to be avoided.

[TurnipEaterDown]

Weight sorting:
The bullet mold is a "sack" that you are pouring lead in.
You want it full of lead only.
You are looking for bullets at the high end. Not the middle of the distribution. Weigh enough "good" bullets and you should see a skewed distribution.
The few higher than the high end of the skew might have a little bit bigger as dropped diameter due to the blocks not being closed as tight, or a small residual sprue, etc. That's not a common distribution characteristic (hopefully).

Without seeing anything, your green band in the chart looks reasonable -- 1.1 gr spread.
You're seeing ~ 0.3% variation.
Normally I would shoot them most likely. To translate -- that's 0.6 gr approximately on a 200 gr bullet. OK w/ me for my 100 yd efforts, but that is for each to decide based on goals.
Target competition, or putting a hole in a deer?

One thing I do w/ group tests:
Get your bullets that weigh in the "good" variance band, and then weigh them out into sub lots loaded over your powder charge increments chosen.
Say you like 0.9 grain spread as your max variance, and you have 5 powder charges. Sub divide that 0.9 grain variance into 5 lots and get 0.2 variance each, then load these sub lots over your charge steps (maybe it's 325.6-.7 over powder charge 1, 325.8-325.9 over charge 2, 326.0-.1 over charge 3, 326.2-.3 over charge 4, 326.4-.5 over charge 5), and use these for groups.
If you have enough, obviously just pick (for example) 326.5gr bullets for every powder charge tested for groups, but my life doesn't often work out that easy, so I was just illustrating another method, given that a person might "pick" 0.9 gr total variance as a personal goal based on tolerable scrap, and yield while maintaining acceptable accuracy.

What I have seen bite me on seemingly good bullets sometimes weighing slightly light is a small amount of rounding at the edge of the band at times -- the bullet "looks good" otherwise, but a hint of roll on the band outside corner. Probably because I often cast with 'a little of this and that' scrap that might be a smidge low on tin or have a contaminant. If I see it I try adding a little tin.

[deces]

Personally, I would just powder coat them all and have a blast for a day.

[garbler]

I’ve always cast with steel molds for forty plus years so my procedure and timing have been pretty much automatic. A friend gave be a two cavity aluminum 45 Lee mold and I gotta tell you I was all screwed up. The mold heated too fast and got too hot most of the time or it cooled too fast. They are a different animal for sure and created all kinds of problems for me trying to get the hang of them. Bottom line is I’m too old to easily learn a new dance step. Just me

Rick

[VariableRecall]

Aluminum Molds are generally more finicky, especially when you're using a 2 cavity mold with high grain weights. They heat up quickly but lose their heat just as fast. You're going to need to pay close attention to how your lead is dropping. You're going to be putting all of your projectiles for the first half dozen casts back into the pot. Check for when knocking the sprues is effortless and you're going in the right direction. Keep your eyes on the infill and how sharp the lines are. Especially for heavy projectiles, ensure that they drop and lay flat instead of on another projectile, where a just dropped projectile may bend out of shape if extra hot.

[uscra112]

Aluminum molds lose heat faster than iron molds. So, this means your casting cadence needs to be a little faster. Another thing to watch is the temp of the steel sprue plate. This will not heat up as fast as the aluminum mold. The hot lead can be cooled passing through the sprue hole, acting just like your mold is not up to temp. Once the sprue plate gets to temp, wrinkles go away and your mold will settle in and start producing good bullets.
Sam Sackett

I learned from a comment by the late Charlie Dell to spill some hot lead over the sprue plate as I take the dipper away. Makes all the difference, especially with moulds for small bullets. (.25 caliber x 65 grain).

And yes, my cadence has to be faster with an aluminum mould, and if I break cadence for some reason I expect some culls before everything is back to normal.

[huntinlever]

I've never used anything other than Accurate aluminum molds so I'm sure it's what you're used to, but I feel pretty solid on the cadence and bullets I throw with them. I just watch the sprue puddle and do a few counts before opening, and check in on the temp as the pot is drawn down (something I used to do but after a longish break, forgot until reminded recently). I generally shoot for about 10 seconds to "set," and 15 to drop. If the puddle starts getting into 20 or more seconds, I know I need to drop the temp (I try to do that, rather than slow down the rhythm in some way). I keep the hot plate going and if for some reason I need to break the cadence I just put the mold on the plate and come back with no issue.

[john.k]

Best move I made was a laser thermometer ......Id been casting too cold for 50 years ,but still getting good bullets ..........lots of casters try to cast too quick and get lots of misshapen bullets ,for which they blame the mould .........Ive got mostly Lee for cost,but I do have some old iron moulds ,which are great .......the iron single cavities are just too slow ,be they Ideal or RCBS..........Lymans are now steel ,and IMHO ,no good.