Does zinked alloy cast small for you?

[Ian]

I don't know why this never came up for me before, but now I gots a problem. 600 lbs of WW alloy that I'm fairly certain is slightly zinked up. I use it for blazing ammo in .45 ACP and other high-volume stuff, no big deal usually because the moulds I use with this batch are big enough to not matter or I'm powder coating the bullets anyway.

BUT, last night I was working through some Lee 500 grain RFN bullets for my .458 Socom and the dang things kept coming out small. No matter how I worked pot temp and alloy temp I couldn't get them up to minimum .457" for powder coating. First batch I cast a few weeks ago with this mould were dropping .4575x4585" on the bands with 50/50 good clippy weights and sticky weights mixed. I pulled some 63/37 assayed solder ingots and added first 1%, then another 1.5" tin to the straight WW mix and it STILL casts small. Got sharper bands without having to go 750 on the pot and hot-dipped frosty galvanized with the mould temperature, but still have small bullets. Not shrunken or hourglassed bullets, just small all over, even on the noses.

This alloy I've used off and on for probably five years, same batch, and it always has a little bit of fillout problem unless the mould is nice and hot. Air cooled and aged it usually comes out about 12 bhn, and does tend to cast small, but I never added any tin to it before, either, and figured that was why (until now). Why didn't tin fatten it up?

 

[popper]

Yes, Sb makes them larger, Sn doesn't

 

[Rick]

Popper is correct, Sn won't fatten them. Can't answer about zinc, haven't used it. In fact always tried my best to avoid it.

EDIT: That was supposed to say "haven't" used it. I fixed it.

 

[Ian]

You both are telling me that straight clippy weights with very little tin content won't cast fatter with some tin added?

Sb/Sn about equal in a Pb base always cast bigger for me than Sb with just trace Sn. Until now. Is the zink sucking up all the tin?

 

[Rick]

I have no idea what effect the zinc may have on tin, I have always gone to great lengths to avoid zinc. I use 2% Sn in WW alloy and get no bump in diameter.

 

[Brad]

No first hand knowledge but based on position on periodic table I would expect Zn to act more like Cu or Al than Sn.
Thinking back on Mike's experience with a Cu In alloys and the age related diameter change I wonder if it is both Zn and concentration related.
That is just a wild ass guess but it is my 2 cents.

You alloy may have just the right amount of Zn to cause this problem. Might try adding a bit more Sb and see if that bumps them back up. We do know that small changes in Sb concentration can cause shrink related issues, why wouldn't Zn do the same?

 

[Ian]

I have no idea what effect the zinc may have on tin, I have always gone to great lengths to avoid zinc. I use 2% Sn in WW alloy and get no bump in diameter.

Interesting. I haven't used much extra tin in my alloys in years, once I got over the "add 2% to everything" mantra. It usually gave my WW 2-3 final bhn points and about half a thousandth girth on a .45. Maybe it was age growth, I know for sure I've been bitten by that more than once with tight-fitting bullets.

 

[fiver]

zinc can cause shrunken band syndrome but you shouldn't see it being a problem unless your seeing oatmeal.

tin will migrate away from lead and antimony and lock onto zinc in an alloy.
but even there the zinc can only take so much away from the other parts of the alloy.
give them a week and measure again.
try another mold.

I add zinc to some of my alloys for the hardness [and inflexibility] it provides .7-1.0% usually doesn't even mean I need to raise the heat.
I just got another 6 lbs of the stuff.

 

[Dusty Bannister]

Ian, when you are casting these bullets that you believe have zinc in the alloy, are you seeing an odd snow flake type of grain appearance on the base of the bullet? Just that sort of crystal pattern on the base of the bullet, around the sprue nub? If you really are having a zinc issue I would expect the bullets to be casting lighter by a small amount than the normal casting alloy in that mold.

 

[Ian]

Not any oatmeal except the normal oxide scum from throwing sprues back in the pot. Problem with this batch has always been flow, the alloy won't fill even Lee's microbands very well unless up over 725 pot temp and running the mould about as hot as can be run without quenching the sprue on a damp sponge (been using the fan on sprues). I'll see if these don't grow some over time, IIRC this alloy usually does that if I don't size them right away.

Dusty, after adding tin the tendency for a fractured crystal pattern reduced to a lightly porous mess (sprue hole too small to flush out oxides from the pour), so yes, without tin the metal acts as you describe. If I cut the sprue too soon it makes a goat-arse pucker like the inside of a crystal geode. I'm going to cast the rest of this alloy out with a different mould and try a different metal with these bullets.

 

[Dusty Bannister]

Thanks for the reply on the crystal pattern. I suspected that is what I have seen from time to time, and while it has not seemed to be a problem when casting larger pistol bullets, I would certainly not want to have that involved in any rifle or when using a correctly sized mold. I never bothered to mic or weigh them since they were always large enough to show that they have been sized when lubed.

I do not have a goat, so can not compare that "aspect".

 

[fiver]

the snow flake pattern would indicate antimony dendrites on the surface to me.

I know the tears he means, you can look right into the base and see the crystalline structure of the alloy.
plus you get little crumbles of lead everywhere.

 

[AMTom]

You both are telling me that straight clippy weights with very little tin content won't cast fatter with some tin added?

They both are wrong.

I spent months of physical testing, under extremely controlled conditions, of dozens of carefully mixed alloys. Tin fattens bullets far more than antimony.

This myth about tin having little to no affect on diameter comes from folks who have just glanced at some inaccurate chart of guesstimated values, or listened to someone who has repeated it.

 

[KHornet]

Total chart followers, often fall short of reality compared to those who
actually test.

Paul

 

[Ian]

the snow flake pattern would indicate antimony dendrites on the surface to me.

I know the tears he means, you can look right into the base and see the crystalline structure of the alloy.
plus you get little crumbles of lead everywhere.

Yep, happens with most all my bullets because they are cast from 50/50 with no extra tin. That's about 2% antimony and usually less than 1% tin, and I cut the sprues at "just" after the smear point so it's easy on the thumb and I don't get bumps. Also the mould stays hotter as often it must with low tin alloy.

Back in the dark ages of my casting career I used mostly Lyman and Lee moulds, most of the time fighting Lyman moulds to get big enough bullets to shoot. I added a lot of tin and monkeyed with pot and mould temperatures a lot to get maximum girth from the Lymans.

Now I don't have that problem unless I choose to, thanks to the products of Tom and others. One thing that I recall is using this exact alloy minus tin to cast some 31-188G bullets a couple months ago and guess what: They cast a nominal .310" on the money, just what the mould spec'd, and they did grow a couple tenths more as they aged (air cooled). So now this has me looking at the Lee mould, which also gets me looking at the 46-470S, which if it isn't made just for the SOCOM then it might as well have been.

 

[Rick]

They both are wrong.

I spent months of physical testing, under extremely controlled conditions, of dozens of carefully mixed alloys. Tin fattens bullets far more than antimony.

This myth about tin having little to no affect on diameter comes from folks who have just glanced at some inaccurate chart of guesstimated values, or listened to someone who has repeated it.

That is wrong! And kind of insulting.

My statement comes from measuring my own bullets cast in the same mold of varying alloys. I've never even seen such a chart with Sn as you mention.
.

 

[Ian]

Total chart followers, often fall short of reality compared to those who
actually test.

Paul

The problem with charts is they are only valid for the person who made them. Variances in equipment, ambient conditions, component temperatures, and individual technique can make bit of difference in the way things turn out.

Rick generates his own data, which is why I was pretty much floored by what he wrote. But he got the results he got, for some reason.

 

[Ian]

That is wrong! And kind of insulting.

My statement comes from measuring my own bullets cast in the same mold of varying alloys. I've never even seen such a chart with Sn as you mention.
.

There's a size vs. alloy chart that I've seen in several of Lyman's cast bullet and reloading books over the years. It's reasonably close, at least it shows an accurate trend if not necessarily take-it-to-the-bank numbers.

 

[Rick]

Yes and I have a chart on my web site but it is an antimony comparison and also states the values are approximate. I haven't seen any such chart referencing tin. Maybe for a reason.

 

[AMTom]

Rick, you are saying that that crude chart on your website comes from your own testing?

You should review the matter.