Just wondering

[Brad]

In a variety of discussions over the past year or more with Rick a common theme comes up. How does tin percentage affect heat treating of lead/antimony alloys. Does increasing tin alter the hardness of a common alloy at a certain temp?

I'm thinking of getting some Rotometals super hard and pure lead to mix to a 5% Sb alloy. Cast bullets from that alloy then add 1% Sn. Cast more bullets and increase Sn to 2,3,4 and 5%.

Test both air cooled and heat treated bullets over a period of time and see what, if any, changes the tin percentage makes. Does tin percentage alter the final hardness based on HT temp? In other words does a 375 F heat treat give the same BHn independent of Sn percentage? What about 400, 425, or 450 F?

I have some ideas on what I will see but don't know for certain. Only one way to know for sure, isn't there?

Anyone else have ideas on what the results will be?

 

[35 shooter]

Well i'm interested in this! I would "think" the more tin added to a common alloy, the bhn would go down a bit, but i've never tried it to see. I don't think the difference would be as much as one might think though, even at 5% tin added.
I really need to invest in a hardness tester.

 

[Ian]

I agree with 35 Shooter, increased tin will reduce the final hardness somewhat when water-quenching. I also think that the time to achieve a stable hardness will be shortened as tin content is increased.

 

[Brad]

I agree that final hardness will be reduced a bit at 450 F. I think heat treat temp will also cause smaller variations as tin increases. The no tin alloy will have the greatest difference in hardness between a 375 and 450 F heat treat, the 5 % tin will have the least.

What really got me thinking is the Cu alloy I mixed up. The bullet I heat treated to 375, 400, and 450 F showed little variation in final BHn after better than 4 months of aging. My range scrap alloy, with much less tin, shows a much wider variation in hardness based on heat treat temp.

 

[35 shooter]

Brad if you don't mind me asking, what was the bhn @450 f with the range scrap alloy? Oh, and if you remember, how much tin was in that alloy?

Btw, good thread! This is hitting all over some things i'm curious about. You know....some of the things that are on my "get off my tale and try list" that i never seem to get around to.

 

[Rick]

Higher percentages of Sn should reduce the final BHN of a heat treated Pb/Sb alloy. I think it should take +5% to do so but that said the vast majority of my HT experimenting has been with a 2% Sn CWW alloy. I did experiment with the same WW alloy and 3% Sn for some time but the only differences I could detect was my Sn was going away faster.

With your 5% Sb alloy most of the gain from heat treating will show in 2-3 days with only minor hardening after that for possibly 3 weeks.

Keep the Pb/Sb exactly the same changing only the Sn percentage in each test, keep careful notes and you should get interesting results.

A grain refiner (arsenic, sulphur etc.) will also increase final hardness tremendously but if you decide to use a grain refiner keep it the same throughout the testing changing only the Sn percent.

 

[Brad]

Looks my at the alloy calculator it might be a bit tough to keep the Sb exactly the same.
If I make a 5% Sb in lead alloy to start then add Sn in small amounts the Sb content will drop a small amount.
Might be 0/5, 1/4.95, 2/4.9, 3/4.85, and I got some foundry Lyman 2 for 5/5.

I'm with Rick, the Sn increasing will drop the ultimate hardness. What I really want to see is how the lower HT temps and hardness are altered.

I have 5 pounds super hard, 20 pounds foundry pure, and a pound of pure tin arriving today. Going to take some time to mix it all up. I will likely be buying a stainless bowl to melt it in.

 

[Brad]

Ok, got the bullets all cast.
I started with 5 pounds superhard and 25 pounds of pure lead. After it was melted I cast 40 Lee 310 gr 44 cal bullets. These were cooled on a slightly damp rag. I then added .25# pure tin and 45 grams of monotype. The monotype helped keep the Sb percentage at 5%, otherwise the addition of tin would decrease the antimony percentage with each addition. This added .85% tin. i then cast 40 more bullets, cooled the same. This was repeated until I had 5 groups of bullets. This took almost 2 full hours to do.

I have 40 each of 0/5, .85/5, 1.7/5, 2.55/5, and 3.4/5 tin/antimony bullets. I will mark them each and 10 of each group will be heat treated at 375, 425, and 450 F for a full hour then quenched.

As cast they measure in hardness as follows in order of tin percentage. 11.5, 15,15,15,22 This was based a single sample from each group. I will test them again tomorrow to see what a little time does for the hardness. Heat treating will be done when I have the time.

 

[Brad]

Damn, this stuff takes lots of time. Got 3 sets heat treated at 450,425, and 400F.

After 24 hours the 5% Sb no tin at 450 F is harder than hell. Measured over 28 BHn on my Cabine Tree. Hardest I have ever tested anything. Can't wait to see what they measure in another day or three.

 

[fiver]

I have a little theory that Tin is actually a retarder to water [precipitation] hardening.
I am super interested in this.

 

[Rick]

I have a little theory that Tin is actually a retarder to water [precipitation] hardening.
I am super interested in this.

It's more than theory but in the percentages "normally" used in cast bullets it's not much of an issue. Get the percentages up over 5% and/or get the Sn much over the percentage of Sb and you'll start to see the difference.

 

[Brad]

I'm heading out of town today. I will try to get some results figured out on Sunday.

I agree with fiver, I think tin reduces the ultimate hardness that can be achieved thru heat treating. What I really want to see is the addition of tin decreases the difference between a 400 and a 450 F heat treated bullet. Is it a big enough difference to be relevant? Don't know.

 

[fiver]

the 4/6/90 alloy I use in several of my boolits doesn't seem to respond to water dropping very well.
I initially thought it was from the tin on the surface "blocking' the antimony water interface.

 

[Brad]

Well, the results weren't very informative at all.
After 12 days of aging the results are sorta in. The 450F batch all pretty well read 24 BHn. The 425 F batch shows a small lowering of hardness in the higher tin alloys but only to 22 BHn. The 400 F group shows pretty much the same hardness as the 425F group across the board.

I expected to see a bigger difference based on heat treat temp. I think the alloys are high enough in Sb to overcome much of the effect of tin, at least at the levels I used. The max tin content was 3.4%, don't know what happens above that level.

What this does tell me is that for this general group of allys that water dropping from the mould would give some pretty consistent hardness. The small change in hardness, if any, between a 450 F and a 400 F heat before quench tells me that bullet temp on quench isn't really critical, at least not in this temp window.

 

[Rick]

In post #9 you mentioned 5% Sb. Are they all 5% Sb, some of them? Like I've said before, it will take over 5% Sn for Sn to start effecting quench hardness.

My 2% Sb, 2% Sn alloy convection oven heat treats to 18 BHN measured on an LBT tester.

Your 5% Sb alloy tested 28 BHN in 24 hours, what are they after the 12 days since?

 

[Brad]

They now measure 24 BHn. To reduce potential errors the last results are based on reading of 3 different bullets for each alloy and temp.

All alloys had 5 % Sb. Tin started at .85% and was increased in increments of .85% up to 3.5%.

The high Sb content made the bullets uniformly hard, that is for sure.

 

[Ian]

Interesting. So keeping the tin below 2-3% makes for uniform cured hardness with a decent quench temp window. No wonder my 50/50 bullets always test so uniform.

 

[300BLK]

The majority of what I've shot over the past 30 years was recovered indoor range lead. The batch that I had tested came back 95.9/2.2/1.9 and casts beautifully. It waterdrops 18-20bhn after about 4 days. Fired from a 40 S&W into a vest over a hardbacked chair revealed a nice mushroom (20+ years ago). Clamped in a vice and hit with a hammer it still seems pretty malleable.

I have about 50% of babbitt 85.9/8.9/5.2 that tests in the 27-28bhn range on my CabineTree tester, and it most definitely is grainy and brittle.

I'm a believer in keeping the Sb/Sn close and as low as possible to achieve the desired hardness. I waterdrop because its convenient.

In trying to make heads and tails of the Cu mixtures, I'm confused if tin is needed at all, and am under the impression that Cu and Sn maybe should be close to the Sb (or less).