How much TIN is needed?

[Marlin Hunter]

I checked (http://www.lasc.us/CastBulletNotes.htm) to see what the minimum amount of Tin is needed to help fill out the mold. I didn't find exactly what I wanted, but I did find this:

Add 2% - 3% tin when casting bore slugs from stick-on wheel weights to aid in mould fill out.

[and]

Linotype and Lyman # 2 alloy's have the lowest hardening potential of common bullet alloys because of the higher tin content (4% & 5%) and lack of arsenic.

It looks like anything over 3% may not be good.

I also want to be able to heat-treat the boolits, or make them harder by water-dropping from the mold.

Can anyone confirm the minimum amount of tin needed for pure lead with some antimony and NO arsenic? If the % of antimony makes a difference, then consider 6-8%.



thanks.

[lwknight]

More than 2.5 to 3 percent tin is waste. Many use 1% and do just fine
More than 5% makes boolits age soften some. 5% casts really nice though.
Most people that I read here use very little antimony. I use 6% to help with drop size and harden the boolits. and use 2% tin to help mold fill. It also lowers your cast temp quite a lot.

More than 7% antimony starts getting up to more brittle boolits.
If for some reason you want to cast really hard bolits like 12% antimony then you need 4% tin so they won't break. Tin is tough, not hard.

You can water drop hot boolits with a low antimony content and make them pretty hard. No antimony is required if you can use soft boolits.

Hope this gives some perspective.

[cbrick]

I checked (http://www.lasc.us/CastBulletNotes.htm) to see what the minimum amount of Tin is needed to help fill out the mold. I didn't find exactly what I wanted, but I did find this:

It looks like anything over 3% may not be good.

I also want to be able to heat-treat the boolits, or make them harder by water-dropping from the mold.

Can anyone confirm the minimum amount of tin needed for pure lead with some antimony and NO arsenic? If the % of antimony makes a difference, then consider 6-8%. thanks.

It's not that over 3% tin isn't good, it's just wastefull and will accomplish little to nothing, at least nothing that your trying to accomplish.

1% to 2% tin is all that is really needed to help control dross, it does this by inhibiting the oxidation of the metal entering the mould and enabling a more complete fill-out of the moulds intricate details. It is not only the surface of the melt in the pot subject to oxidation, the stream of alloy from a bottom pour pot (or a ladle) is also in contact with oxygen and this is where tin has it's largest benefit in reducing oxidation and aiding better mold fill-out, from the spigot to inside the mold. For tin to increase age softening the percentage would need to be upwards of 6-8% or more, that much tin could also increase the amount of time to acheive full hardness.

6-8% antimony is getting up in brittleness, some use lino at 12% antimony but there will be no expansion on game and it can and does shatter on steel targets. 3-5% antimony will HT with a good hardening time curve, the lower the percentage below that the longer the time required for full hardening. Arsenic in itself adds very little hardness but it acts as a catalyst with antimony increasing the amount of hardening that can be acheived far beyond what the percentage of antimony would suggest.

Bottom line: Tin up to 2% and antimony around 4% should be close to WW alloy at 10-12 BHN and could be quenched to around 17-18 BHN.

Rick

[Nora]

I will use just enough to get good fill with WW. My ingots are 1.75# muffins. Using .125" 95/5 lead free solder I'll add 1.5" per muffin (ruffly .08 oz) when topping of the pot. Mine is a Lee 4-10, so I've cut it up into 1.5 and 3" lengths. That also helps keep the math simple.

Nora

[Nora]

1% to 2% tin is all that is really needed to help control dross, it does this by inhibiting the oxidation of the metal entering the mould and enabling a more complete fill-out of the moulds intricate details. Rick

I thought the tin gave better fill out by reduced the surface tension of the molten metal? And that the carbon from the flux used worked to reintroduce the oxidized lead back into the mix? (I'm not trying to contradict, I'm asking because I don't know)

Nora

[sqlbullet]

reduced the surface tension

True. Have confirmed this many places.

to reintroduce the oxidized lead

Not sure. Have read conflicting reports, and am not a metallurgist or a chemist. It is possible in my mind that an oxygen reduction reaction occurs, but I have no idea if that is true. Perhaps someone with more/different letters than I could comment?

My practice is to add only the amount of tin required to get good bullet fill out at 675° casting temp. That usually works out to about 1-1.5%. I have a goodly supply of tin, but given the price, I am not inclined to waste it.

[sheepdog]

Honestly I find as long as I have the heat right tin isn't needed. IMHO tin makes up for lack of mould temp, nothing more.

[montana_charlie]

1% to 2% tin is all that is really needed to help control dross, it does this by inhibiting the oxidation of the metal

I'll look back in of and on (over the next few days) to see the explanation of how that works...and read the linked article.
CM

[cbrick]

I'll look back in of and on (over the next few days) to see the explanation of how that works...and read the linked article.
CM

Read this article Charlie, perhaps it will help you understand how it works. Cast Bullet Alloy's

I thought the tin gave better fill out by reduced the surface tension of the molten metal? And that the carbon from the flux used worked to reintroduce the oxidized lead back into the mix? (I'm not trying to contradict, I'm asking because I don't know) Nora

Your right, tin reduces the surface tension by keeping the oxidation at a minimum. It's not two different things, it's the same thing.

Fluxing does reduce oxidized metals back into the melt.

Rick

[montana_charlie]

Read this article Charlie, perhaps it will help you understand how it works.

Thanks for the link, Rick. Now I see where you got that.
The author tells 'what' happens (according to his understanding) but he doesn't say 'how' it happens that way.

I'll reserve judgement (and comment) until I do some more looking around, but I don't think he has it quite right.
I base my skepticism on reading some of those 'lab reports' where the people doing the work have strings of letters after their names...and you have to convert all of their temperature data from Kelvin (or something) into Farenheit to know what is actually being said.

I tried hard to read it with good understanding, and came away thinking I had a pretty good handle on oxidation within lead/tin alloys. If I can ever find it again, I'll let you know.
CM

[StarMetal]

In my opinion and casting/shooting for years, tin use is another over rated thing. I agree with the school that anything over 2 % is a waste.

Joe

[cbrick]

Thanks for the link, Rick. Now I see where you got that. The author tells 'what' happens (according to his understanding) but he doesn't say 'how' it happens that way.

I base my skepticism on reading some of those 'lab reports' where the people doing the work have strings of letters after their names...and you have to convert all of their temperature data from Kelvin (or something) into Farenheit to know what is actually being said. CM

The article was written from several of those "lab reports" from the metals industry. I know because I read them all over and over again as I wrote the article.

How does it do it? There are people that can explain crytalline structures and such in detail but as a boolit caster it's good enough for me that 1 or 2% tin does reduce the surface tension by limiting the oxidation of the melt. Increasing the temp increases the rate of oxidation and the benefits of tin are greatly reduced much past 750 degrees. Increasing the tin percentage lowers the melting point, reduces the amount the alloy can be hardened (assuming antimony) and increases the rate of age softening.

Rick

[montana_charlie]

The article was written from several of those "lab reports" from the metals industry. I know because I read them all over and over again as I wrote the article.

I see.
You didn't link to the article as 'support' for your comment...you wrote the article.

as a boolit caster it's good enough for me that 1 or 2% tin does reduce the surface tension by limiting the oxidation of the melt. Increasing the temp increases the rate of oxidation and the benefits of tin are greatly reduced much past 750 degrees. Increasing the tin percentage lowers the melting point, reduces the amount the alloy can be hardened (assuming antimony) and increases the rate of age softening.

I agree 100% with everything you just listed...except for the "by limiting oxidation" part. I'm not convinced that is how tin makes the alloy 'wetter'.

I can't say I 'disagree', but it doesn't fit with what (I thought) I 'knew fer shure'.
I think the addition of tin would cause the alloy would see just as much reduction in surface tension, even if it was in an oxygen-free environment where oxidation could not occur.
Perhaps you have some links to those lab reports you researched when writing the article...

On the other hand, it's a small difference of opinion, so you may not want to pursue it further.
CM

[lwknight]

Pure lead will oxidize more (or maybe just faster) than lead with a little tin in it, whether its molten or stored as ingots or boolits. The oxidation is only on the surface so. its no big deal either way.
You don't get the black finger so much handling tin alloy as pure lead either.

[Marlin Hunter]

The article was written from several of those "lab reports" from the metals industry. I know because I read them all over and over again as I wrote the article.

How does it do it? There are people that can explain crytalline structures and such in detail but as a boolit caster it's good enough for me that 1 or 2% tin does reduce the surface tension by limiting the oxidation of the melt. Increasing the temp increases the rate of oxidation and the benefits of tin are greatly reduced much past 750 degrees. Increasing the tin percentage lowers the melting point, reduces the amount the alloy can be hardened (assuming antimony) and increases the rate of age softening.

Rick

Is that kind-sorta-but-not-really-like adding salt to water to raise the vapor pressure and reduce evaporation.

[rob45]

It's not that over 3% tin isn't good, it's just wastefull and will accomplish little to nothing, at least nothing that your trying to accomplish.

6-8% antimony is getting up in brittleness

Rick

Some good responses on this thread. I certainly agree with the information presented. I realize Marlin Hunter started this thread in concern to using tin as an aid in casting, but I have a question concerning the use of tin as it relates to bullet integrity.

Allow me to give a little background concerning my situation.
I have spent the past several years doing dedicated research and testing on the modern 45-70 loads, specifically with pressures associated with the Marlin lever actions. A friend of mine is into wildcat cartridge development, and owns one of those "portable ballistic labs" that utilize strain gages and software. I use the T/C Encore as a test mule to develop the maximum pressure loads before transferring the loads over to the levers. (Not only is testing easier, but if I really mess things up with insane pressure, a stretched frame is easier to replace than a levergun!)

The loads are developed specifically for hunting purposes. I realize that there are commercial outfits who specialize in this, and some may consider me to be "reinventing the wheel". But I prefer to develop loads specific to my situations, rather than settle for a few choices from the manufacturers. I have developed loads from mild to wild, 250 grain bullets to 550 grains in various designs, both jacketed bullets and cast. However, my most-tested loads involve the bullets around 350 grains at velocities above 2000 fps. Not that these are my "everyday" loads (ouch!), but I purposely attempt to push the bullet to its limits. The number of various alloy combinations I have tried are mind-boggling.

The major stumbling block has been finding the correct alloy for desired terminal ballistics. Something I have definitely learned is that the alloy that may seem ideal for the load (accuracy/control of leading) is not always ideal upon impact, dependent upon the desired characteristics.

Most of my testing is done with wet paper, simply because that is the most accessible and economical for me. I feel that it is a good standard, comparatively speaking. I have done one test with ballistic gelatin, but that was to get an idea of "wound channel" to see if the paper testing was leading me in the right direction.

One of the early tests involved comparing Lyman's No.2 (5-5-90) against the hardball alloy (2-6-92). The two different alloys react the same as far as the load goes, yet recovering the fired bullets revealed better weight retention with the No.2 alloy.
Drawing conclusions from that, later testing was done with wheel weight metal from a 800 pound lot. This lot had a tested composition of 3.2% antimony and .18% tin. Following the accepted procedure of incrementally adding tin, the bullet recovery testing showed the same trend- better weight retention and penetration whenever I added tin.

I am not a metallurgist, so I can only base any conclusions upon the old "try it and see" methods. I make every attempt to be very methodical in my testing. Every lot of lead in my shed is of known composition. The loads are developed so as to ensure similar impact velocities; I even use the chronoghraph as I'm firing into the test medium just to make sure. Even with low-grade antimonial alloys (as low as 2.3%), the trend seems to be better weight retention as the percentage of tin is increased.



My questions are:

1. Can anyone explain what is actually happening concerning the effect of tin as it pertains to alloy integrity? I am not interested in the effects on casting characteristics, nor am I concerned with hardening/softening characteristics. I want to know why the bullets are holding together better after impact. The additional tin seems to help counteract the effect of the antimony; is this what is actually happening, or am I way off base?

2. Are my findings in line with what should be happening "in theory"? If not, maybe I need to reconsider my approach.

3. Keeping in mind that these alloys contain some amount of antimony, is the above quoted 6-8% the starting point of actual brittleness, or is it the accepted standard of what is considered to be brittle for our normal range of utility? My reason for asking is this: If my WW metal mentioned above only has 3.2% Sb, why does it consistently shed more weight than 10:1 lead/tin alloy? The two alloys are nearly identical in initial hardness, but the 10:1 cannot be quenched or heat-treated to a high enough level of hardness to prevent leading. However, I did indeed run a test between the two in their as-cast state at 2200 fps just to see how they held up on impact (and dealt with the leading afterwards!) The WW retained 62% of its original weight; the 10:1 retained 83%.
This has led me to believe that the introduction of any antimony begins to introduce some degree of "brittleness"; it's just that we do not consider it to be a problem until it reaches above our accepted level of compromise, i.e., when we easily start noticing the difference.

4. Does anyone else have any experience similar to my findings above?


I am open to all thoughts pertaining to this topic.

[lwknight]

Rob, I might have a few points that I thought could be worth a considering and might help figure out this quandry. Till a real metalurgist happend by.

1. Tin is harder than lead.

2. Lead with tin in it is harder and tougher than pure lead.

3. Tin and lead are a true alloy.

4. Lead and antimony mixed is nothing more than a mix of antimony suspended in lead

5. Lead with antimony in it seems hard but the crystals will tear apart because the lead is not tough and does not bind them together. Therefore lead with a lot of antimony is just brittle.

6. Tin will chemically bond with antimony like it does copper or brass. Therefore in effect soldering the antimony crystals together. Maybe. Just a thought.

More tin will make the boolits more mallable and antomony makes them harder so why not the best of both worlds. I think thats where Lyman came up with their #2

I think that the "Hardball" mix was a commercially used recipe because years ago antimony was cheaper than tin and by using less than 1/2 the tin and a 20% more antimony they saved money and still could tout "hard cast bullets"


Why do we need lead at all? other than the price if tin is prohibitive. I do not have any pure antimony to try to alloy with tin just to see what happens. I'm sure somebody around here knows the answer on that already.

[lwknight]

Just for kicks I melted a 4oz 30% SB with 2oz SN to get Pb43-Sb20-Sn37 and casted into a bollit. I beat it down to 1/8" with a hammer and did the same with a 92-2-6 boolit.

I cut off the ends of both with nippers and could not tell one bit of difference either by cutting pressure or hammering. neither were brittle at all and in the mixture the antimony did not slush up like it does without tin.

To me this is evidence that tin does bond with Sb and holds it suspended in the lead.

[HORNET]

rob45, If you go back to the main index page and go into the Classics and Stickies forum (at the top), about 6 threads down is one titled "Toughness of Lead-tin-antimony Alloys" by Grumpy One. It runs several pages and has a lot of test results and explanations of the metallurgy that I think you're looking for. A very interesting read.

[lwknight]

I did just prove to myself that the hardness of antimony can be counteracted by excessing amounts of tin.