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Thread: effect on hardness of lead with antimony and tin

  1. #1
    Boolit Master
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    effect on hardness of lead with antimony and tin

    There has always been discussion here about what is the hardness of a lead mixture with certain amounts of antimony and/or tin. I don't have a simple formula for that.

    Some years ago, I got a bunch of almost chemically pure lead (roofing lead). I also had pure tin and a bunch of monotype with a set quantity of antimony in it. At the time, I also had three hardness testers (SAECO, Potter, and Lee). They all had different scales, but I was able to use them for cross referencing. So I did a bunch of experiments mixing small amounts and testing them for hardness. This is what I found.

    1) Pure lead is not Bhn 5. I understand that chemically pure lead is Bhn 4.5. The stuff I had was Bhn 4.6 to 4.7. If it tests at Bhn 5, it already has unknown amounts of antimony and/or tin in it. That affects the final hardness.
    2) Very small amounts of antimony added hardness very quickly, but its affect was reduced the more that was added. In other words, a graph of percent antimony vs hardness went up very quickly at the start, but the line bent downward and plateaued fairly quickly. At small percentages (like 1%-2% or so), it added a lot of hardness, more than one Bhn for each percent. Anything over about 15% to 18% did not add any measurable hardness. I have not really seen this trait mentioned here before.
    3) Tin added hardness on almost a linear fashion. Tin seemed to add very close to 1Bhn for each 1% of tin. The graph also bent downward like the antimony line, but not nearly as quickly. Even at 15%-20% it was still adding part of a Bhn for each additional percent.
    4) I was not able to tell anything about the relationship with both tin and antimony. That was too complicated for my instrumentation. However, I did decide that when I had a certain amount of antimony, I should have at least an equal percentage of tin. Less than that amount of tin, the casting became harder (more rejects) and the bullet was more brittle.

    I have a bunch of experiments recorded that I turned into a rough graph for Bhn prediction purposes. It does not seem to be any better than the other formulas that I have seen posted here from time to time. However, it does not seem to be any worse, either, and since I spent a lot of time on it, I use my graph.

    Anyone have any comments.

  2. #2
    Boolit Grand Master
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    Tin does wonderful things for casting lead alloys. I had never used Lyman #2 alloy prior to a friend buying some to cast bullets for his 41 Magnum with. OMG, how nice that stuff is to work with compared to most other alloys! Its only down-side is that tin costs the earth to add to a mix, which is why 92/6/2 with similar hardness gets a lot of use. Linotype is nice to cast with as well, likely owing to its 4% tin content.

    I have a lot of 92/6/2 on hand currently, also a good amount of unalloyed lead. I bought 20# of tin a few years ago from Rotometals, and made up some 30/1 Pb/Sn just for grins (and my 38/55 levergun), and added 12 oz of Sn to 20# of 92/6/2 to make some Guerilla Lyman #2 with. Oh, does it ever cast nicely. The 30/1 runs nicely as well.

    Just some random thoughts prompted by Harry's posted alchemy.
    I don't paint bullets. I like Black Rifle Coffee. Sacred cows are always fair game. California is to the United States what Syria is to Russia and North Korea is to China/South Korea/Japan--a Hermit Kingdom detached from the real world and led by delusional maniacs, an economic and social basket case sustained by "foreign" aid so as to not lose military bases.

  3. #3
    Boolit Master
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    I have never tried the 92-6-2. With the ingredients I have, I mix up whatever I need.

    PS. Tin doesn't cost much for me, so I use more than absolutely necessary. You might say I am wasteful. My wife is addicted to estate sales. Luckily, she does not spend much there. I think she does it just to look at houses. Whenever she runs across cheap solder there, she buys it for me. I melt it down and cast it into 0.690" balls so that I can add it to the mix in specific amounts. I figured out once that the tin I use cost me about $2 to $3 per pound. I probably have enough to last the rest of my life. The more tin added, the nicer it is to cast with, as long as it does not get too hard. With my 41LC, I make sure not to put more than 40:1 in.

    PPS. The lead I use cost about a quarter ($0.25) per pound. I bought about 1,200lbs when they were tearing down a bunch of 100 year old buildings for urban renewal about 30 years ago (it took 3 trips with the car). It was roofing lead and very soft (pure). I still have about half of it. I don't think I am going to last an additional 30 years.

    PPPS. About 250lb of monotype was given to me about 25 years ago. I use it sparingly. Not because of the cost, but because it is nasty stuff. It certainly does harden things, but harms everything else that has to do with casting so I don't use it unless a lot of hardness is absolutely necessary.

    One of the things I was wondering is if anyone else has noticed the effect of antimony: My observation that it adds a lot of hardness in small amounts, but the effect quickly reduces as the amount increases. I don't believe that I have seen that mentioned before.

  4. #4
    Boolit Master 243winxb's Avatar
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    Rotometals-
    Basic Rules for Hardening Lead-

    For every 1% additional tin, Brinell hardness increases 0.3.
    For every 1% additional antimony, Brinell hardness increases 0.9.
    For a simple equation,
    Brinell = 8.60 (Antimonial Lead) + ( 0.29 * Tin ) + ( 0.92 * Antimony )

  5. #5
    Boolit Master
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    243winxb: That's the problem I have. The formula you post (and all the others that I have found and tried) show a straight-line relationship between hardness and amount of antimony/tin. That is not true according to my experiments.

    A change of antimony from 1% to 2% (+1%) does NOT give the same hardness change as does going from 10% to 11% (+1%). From my experiments, the change from 1% to 2% will give a much larger Bhn change than will a change from 10% to 11%. And, if you go from 20% to 21% (+1%), there will be absolutely no change in hardness. The affect of tin is different, but similar.

  6. #6
    Boolit Buddy Petander's Avatar
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    Here is my 18 BHN alloy XrF:

    Click image for larger version. 

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    It is a WW/Monotype/22 scrap mix, I wanted to see what contaminants I have. It casts very well despite the high antimony content.

  7. #7
    Boolit Master Grmps's Avatar
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    I read somewhere that adding equal parts tin and antimony creates anew "matrix" which is harder than calculating adding tin and antimony individually. That's why they're several recipes with equal parts tin and antimony.

  8. #8
    Boolit Master
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    Petander: I once tried casting straight monotype. From memory, the sticks I have had 19.5% antimony and 8.5% tin. The bullet did not have provisions for a gascheck (Lyman 375167). Unfortunately, crimping the cases into the bullet at loading cracked most of them. Even the ones that did not obviously crack would break when moving the cartridge from the magazine to the chamber. I remelted all the bullets and started adding tin. I ended up with a mixture of about 70% lead, 15% antimony, and 15% tin. The bullet was easier to cast, held together well, and was over 30 Bhn. Shortly afterwards, I found a really good deal on jacketed softpoint bullets for it. So, I bought a bunch, stopped casting bullets for that gun, and sold the mold.

    Grmps: I believe you are right. It gets complicated very fast. If it was simple, there would not have to be as many "casting experts" as there are.

    Also, I do not believe that the change in Bhn is a straight line relationship (like the formulas say) for either antimony or for tin. My experience is that with very small percentages of antimony (say below 4% or so) the actual tested Bhn is MORE than what the formula says. In midranges (say 4% to 6 or 8%) the formula and the test are pretty close. For high ranges (over 6 or 8%) the test Bhn is LESS than what the formula says. Tin is somewhat the same way, but less pronounced. The mixture of both of them is too complicated for me to accurately predict.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check