Questions

[Frank]

1) Mold A gives me shiney bullets. I can raise the temp to over 850 and they will still be shiney. Then I switch to Mold B, use the same temp as Mold A, 800'F initially, and the bullets are frosty. Same alloy, just switched molds. Mold A is a single-cavity aluminum mold, and mold B is a double-cavity aluminum. I thought the temp of the alloy is what made frosty vs not. Maybe it's because I pre-heated Mold B on the hot plate too much. But even after casting alot, the bullet is still more "gray" than the other, which are all still shiney. The first few of Mold B were a little bubbley.

2) Why is it that I have to cast at 800-820'F with 94/6 ingots in the pot with 2% tin to make a wrinkle-free bullet, but when the pot goes low and I add straight WW's, the casting temp drops? I thought that the heavier lead concentration would have required higher casting temperature and WW's are supposed to be a higher lead content than 94%. Could it be that the 94/6 alloy I bought isn't really that mix?

[sqlbullet]

1. Mold temperature. I actually think frosting is related to the temperature of the bullet when exposed to air. However, in order to accomplish that you usually need a hot mold and hot lead. I can get frosted bullets on the first cast from a 650° pot if I have a really hot mold. Be interesting to cast into a hot mold, then let the bullets completely cool in place and see if they are frosty when dropped.

2. I am not sure how antimony content effects bullet fill out, but your empirical evidence would suggest it has a negative effect. Tin reduces the surface tension to promote better fill out.

[theperfessor]

1. Mold B was probably hotter than mold A throughout your casting session. Think about it this way - mold B is getting twice the hot metal poured in it compared to mold A. Mold B does not have twice the mass (to absorb heat) or twice the surface area (to lose heat) of mold A, so mold B must be hotter.

Frost comes from having both alloy and mold too hot, and degree of frosting varies with alloy composition. It's cosmetic only, consistency and good fillout is all that really matters.

2. WWs vary, your 94/6 is probably OK. Somebody else may have more insight here.

[runfiverun]

mold b holds twice as much lead.
the arsenic in the ww's helps it fill out too.
tin and such isn't/aren't the only answers to fill-out.

[cbrick]

2) Why is it that I have to cast at 800-820'F with 94/6 ingots in the pot with 2% tin to make a wrinkle-free bullet, but when the pot goes low and I add straight WW's, the casting temp drops? I thought that the heavier lead concentration would have required higher casting temperature and WW's are supposed to be a higher lead content than 94%. Could it be that the 94/6 alloy I bought isn't really that mix?

theperfessor did a pretty good job on question #1.

Question 2 is a bit fuzzy. Are you referring to pot temp after the WW's are completely melted and the melt is back up to casting temp? If so, by how much?

Every electric pot that I have ever used would increase the temp as the level of alloy in the pot decreased. Adding an alloy would decrease the temp until the new alloy is completely melted and back up to proper temp.

The 3% or so difference in your 94/6 alloy I wouldn't think make much difference. The pot itself has a thermostat that shuts off when a pre-set temp is reached and shouldn't make any difference to the pot what alloy is in it. If it's set to shut off at 800 degrees it will shut off at 800 degrees if it has 800 degree lead or 800 degree of something else in it.

Or are you saying that you need to cast at a lower temp with the WW? A good rule of thumb is to cast at about 100 degrees over liquidus temp of the alloy for good boolit fill-out. Some moulds may need some more heat; aluminum will dissipate heat much fast than steel for example.

So I'm a little confused on what question #2 is.

Rick

[Frank]

cbrick asks

Or are you saying that you need to cast at a lower temp with the WW?

Correct. I try to cast at the lowest temp required. WW's didn't even heat up more than 760 with the dial turned on and it works great. But if i put 94/6 in there and try to do the same, it freezes over, poor fillout, etc. Even at 800, it wrinkles, so I add tin and it's OK, but I'm casting at 830F. I know every session is different. I shoot for 5-6 seconds until the sprue is hardened seemed to work good. But I was curious. I thought as you approached pure lead, casting temps increased. One would think then that it would be the opposite of the above. Then Riverrun says

the arsenic in the ww's helps it fill out too.

Well they you go. So it's not just lead concentration that affects casting temp required, it's the arsenic content? OK, I'll buy that.

So when WW's run out and everybody has to buy it, does that mean that casting temperatures will have to be 800-900F? I guess that's OK too, right?

Perfessor says

1. Mold B was probably hotter than mold A throughout your casting session. Think about it this way - mold B is getting twice the hot metal poured in it compared to mold A. Mold B does not have twice the mass (to absorb heat) or twice the surface area (to lose heat) of mold A, so mold B must be hotter.

Frost comes from having both alloy and mold too hot, and degree of frosting varies with alloy composition. It's cosmetic only, consistency and good fillout is all that really matters.

Thanks. I get it now. I kind of like the shiney bullet look. Any they are definitely MORE CONSISTENT in weight, the single cavity.

[shotman]

Well we cover the heat problem. You say 94/6 do you know for sure? many times the people selling lead say they are WW or Pure. WW can be anything that was on a wheel Pure can be anything that is not a ww. I dont buy it if I dont know for sure. I make shot and a mix will really mess a shotmaker up fast. Zinc will melt and mix with the lead mix . In a boolit pot the zinc will tend to seperate and float if it was a mix. If you flux it back in and start to get crappy boolits you will see. Let it float and skim off.

[theperfessor]

Are you casting rifle bullets? I know a lot of rifle shooters use single cavity molds because of the consistency factor. Sometimes they also use one cavity only in a two cavity mold, or mark one cavity in a way that helps them separate the bullets later. I'm not sure you could keep a two cavity Lee aluminum mold hot enough by just using one cavity but I've never tried it and I could be wrong. I know you can use one cavity of a Lyman or RCBS iron/steel two cavity mold successfully.

The surface texture and composition of a bullet depends on three principal factors.

(1). Mold surface texture. Let's assume your molds have mirror smooth surfaces, so we'll throw this out as having any effect on the bullet.

(2). Material composition and (3) temperature and cooling rate. These go hand in hand.

A pure element has a single melting/freezing point. Depending on the alloy system formed by combining metallic elements, most alloys have a range of temperatures where the material solidifies. An exception to this is a eutectic alloy, where the exact composition/ratio of metallic elements have a single melting point.

As an alloy cools, the cooling rate determines the time it takes for the bullet to cool. The longer it takes, the more time there is for the material with the lower freezing point (which is still mostly liquid) to be pushed into the interior of the bullet, leaving the surface material to consist of a higher concentration of the material with the higher freezing point. Some of the lower freezing point material is trapped in the solidifying surface and a dendrite (a somewhat tree-like structure) is formed. Think of moisture from the air that condenses on a window and grows into frost as it freezes.

If your alloy will permit it do as cbrick says - cast at 100 or so degrees above the liquidus (highest melting point) temperature. Sometimes you can add tin for better fillout at lower temps, but sometimes, especially with low mass aluminum molds you just have to crank up the temperature and live with a little frosting.

[Frank]

You say 94/6 do you know for sure?

Yeah, it's stamped right on the ingot.

[lurch]

Call me crazy, but I thought that one of the reasons shot contained a bit of Sb was to increase the surface tension of the alloy, promoting easier formation of rounder shot as it fell in the tower. To me that makes an alloy containing Sb harder to get fill out with and requiring somewhat higher temperature for best fill out, all else equal.

Am I wrong?

[theperfessor]

I thought Sb was used in shot to make it harder when quenched? A lot of casters use high Sb shot to raise alloy hardness, especially when water quenched. Don't know if it increases surface tension or not. I know zinc sure will.

[Frank]

Sometimes you can add tin for better fillout at lower temps, but sometimes, especially with low mass aluminum molds you just have to crank up the temperature and live with a little frosting.

It's kind of funny because the "low-mass" Lee mold is filling out fine out lower temps, with WW's, 750F. It's the other mold with the 94/6 ingot that has problems, it has to go higher temp. Is there a temp limit on when you shouldn't add tin?

[Frank]

sqlbullet said

1. Mold temperature. I actually think frosting is related to the temperature of the bullet when exposed to air. However, in order to accomplish that you usually need a hot mold and hot lead. I can get frosted bullets on the first cast from a 650° pot if I have a really hot mold. Be interesting to cast into a hot mold, then let the bullets completely cool in place and see if they are frosty when dropped.

2. I am not sure how antimony content effects bullet fill out, but your empirical evidence would suggest it has a negative effect. Tin reduces the surface tension to promote better fill out.

Hey lurch, maybe sqlbullet got it right. Oh, never mind, he got the evidence from me.

[lurch]

Call me crazy, but I thought that one of the reasons shot contained a bit of Sb was to increase the surface tension of the alloy, promoting easier formation of rounder shot as it fell in the tower. To me that makes an alloy containing Sb harder to get fill out with and requiring somewhat higher temperature for best fill out, all else equal.

Am I wrong?

Doing my best Homer: DOH...! Stupid me being up too late and trying to post with the thinker disengaged. I meant As as opposed to Sb.


I know that the Sb content will make the alloy harder and harder still (for a while...) if age or precipitation hardened. As seems to promote this even further.

The bit about the As increasing the surface tension some is something I believe I read somewhere along the line but can't put hands on right now.

Just wanted to see if anyone else had seen that.

Kurt