Do Pb, Sn and Sb Stratify or Separate in the Melt?

[Buck Shot]

Fairly new guy to casting here, and I suspect this has been discussed, and I did a search but didn't find what I want.

Question: If you have a bottom-pour pot of molten alloy at around 700°F with lead, tin and antimony in it, will the three metals tend to stratify (maybe according to their density) or otherwise separate if you don't stir the pot from time to time?

The reason I ask is, I just cast a couple of batches of boolits, and some came out frosty, and others came out shiny. (I haven't checked them for hardness; I'm still learning about that.) Is this more a function of the temperature of your melt and your molds, or is it due to the heavier metals coming out first and the lighter metals coming out later ... or both?

If it matters, I was using about 7/8 range scrap with about 1/8 foundry type (by weight) thrown in.

To add a few more variables to the mix, I was also using new molds ... an aluminum N.O.E. and an aluminum Lee. I cleaned them well and degreased with brake cleaner, then sooted them with acetylene. Was also careful to lube them with 2T oil following the instructions I found here on this great site.

Thanks in advance for any information.

[reddog81]

Frosty versus shiny is an function of temperature. Frosty means the mold is getting pretty hot.

I’m not sure how or when or under what conditions the various metals would separate. I’m interested in hearing what others have to say about it though.

[Dusty Bannister]

No, they do not stratify. See the following link, specifically para (2)

http://www.lasc.us/CastBulletAlloy.htm

[mehavey]

No stratification, no separation, once in a melt and stirred.
You just have hot-bullet frosting.
They shoot the same....

[quail4jake]

What Dusty said... LASC! pay close attention to the Sb-Sn system, get a PhD in metallurgical engineering with a strong emphasis in non ferrous alloying and crystal systems and call me in the morning!

[LenH]

Don't worry so much about hardness. Fit is King, all else is secondary.

[ioon44]

Don't worry so much about hardness. Fit is King, all else is secondary.

Totally agree with this.

[country gent]

One other thing is as the volume drops the same setting is heating less mass so a higher temp and possible frosting

[Larry Gibson]

Suggest you down load the Lyman #3 Cast Bullet Handbook and read The Metallurgy of Molten Lead Alloys by Marshall. A bit dry and technical but will give you the answers.

Basically your alloy [7/8 range scrap with about 1/8 foundry type (by weight) thrown in] is antimony rich and tin poor. Antimony will blend with tin in equal proportions up to about 5% each in a ternary alloy and stay in solution with the lead. The Sn & Sb for the submetal SbSn which will stay in solution up to the 5% in lead. It will not separate or "cook out" as many think. In you antimony rich alloy the antimony not in solution with the tin as SbSn with harden or "freeze" first. That is most often the "frost" you are probably seeing and should not be confused with the "frost" from too hot a mould and/or alloy. At 700 degrees with a reasonable casting tempo you should not get "frost" on any bullets with a ternary alloy having the antimony and tin in balance (equal amounts).

I also suggest re-cleaning the moulds and not "smoking" or "sooting" with anything. A clean naked mould [except for lube on the sprue plate] will cast the best bullets.

[Buck Shot]

Thanks for all your replies, everyone. I appreciate your help, and will look into the sources you suggested.

[lightman]

Someone once said that once you pour the Jack into the Coke you can't get it back!

[jimb16]

If you don't flux your metal occasionally, you can loose a little tin, but it isn't a serious loss. Just flux now and then and you should be doing that to keep your best casting anyway. Otherwise, the metals do not separate. You have an alloy, not a mixture.

[carelesslove]

Buckshot, carelesslove, here !

I have been casting handgun bullets for 45+ years. IMHO, you just received more solid direction on this subject than I was able to gather in 35 of my 45 casting years.

For many years, I fluxed way too often - thinking that keeping the pot fluxed kept the lead / tin, and antimony all mixed up properly. After initial alloying and the initial fluxing, my additional fluxing just cleaned the alloy of dirt that wasn't there!

LenH has provided a real nugget - "Fit is King, all else is secondary". For my revolvers, fitting the bullet to the cylinder throats made everything work better - even when the alloy was soft.

I have shot a lot of frosted bullets with no problems. They are kind of pretty.

Tom "carelesslove" Love

[Buck Shot]

Thanks again, fellas, this is all good info. I appreciate it.