This is for the “what it is worth” Dept. You get what you pay for.
Black powder shooters often describe their bullet hardness in the ratio of lead to tin as in 20/1 and it is clear that many people don’t have much of an idea beyond those numbers what that might mean with regard to alloy hardness. It is said that 30/1 is soft and 20/1 is harder and 16/1 is really really hard. Oh, it is also said that wheel weight alloy is some amount much harder than what can be expected to work at all.
Brinnell Hardness Number (BHN)
BHN is a measure of yield strength or in other words, the resistance to a load placed upon the metal. It is determined by the amount of kilograms that can be supported by one square millimeter of metal surface.
Common BHN measurements:
Pure lead is said to be 5 BHN but lab grade is 4.+ something.
40-1 Lead-tin, 8.5 BHN
30-1 Lead-tin, 9 BHN
20-1 Lead-tin, 10 BHN
16-1 Lead-tin, 11 BHN
10-1 Lead-tin, 11.5 BHN
Linotype, 22 BHN
Lead/linotype, half and half, 15 BHN
Lead/Tin alloys loose their hardness over time. This lose resembles the right side of the bell curve. The greatest loss occurs in the first days and week(s) after casting. Post 40 days and the hardness loss is so small as not to be measured on a LBT tester.
Lyman No. 2, 15 BHN After 6 weeks, air cooled bullets will reach maximum hardness. Heat-treating can further increase this hardness.
Freshly cast wheel weight (ww) is 8 BHN, aged at room temp. after two weeks it becomes 12 to 13 BHN, and ww composition varies only a little. Heat treated wheelweights, 18-35 BHN, varies with heat-treating and composition.
Alloys with about equal amounts of antimony and tin, cast and air cooled, at least in the range of 94-3-3 percent do not change much over time. That is, they do not age soften or harden. So, if you think hardness is important to your load accuracy this might give you some food for thought. Contrary to what is so often repeated, antimony does promote alloy flow and picks up the detail in the surface of the mould cavity.
As you can see from the information above, there is not a heck of a lot of difference in hardness between the common lead/tin alloys we BPCR shooters use. That is why when we hear that a specific rifle is married to a given lead/tin ratio I wonder Hmmmmm, maybe. It is good to keep an open mind BUT, what are the other uncontrolled factors that might have lead the tester to believe the greater or lesser alloy ratio might be the cause for the performance difference with in the load?
Just something to think about and stir up the pot. (I know-bad pun)
The best explanation of bullet alloys, their hardening, softening, time dependent stability characteristics that I have ever read can be found in:
The 1991 Jan-Feb issue of the Fouling Shot has an article by O.H. McKagen and Dennis Marshall entitled "On Lead-Tin Solders".
Michael Rix
Bullet Hardness
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Michael Rix
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Bullet Hardness
"Vegetarian" Old Indian word meaning lousy hunter.
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MLV
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Mike I'd like to chime in here with a little story. Back when Steve Garbe and I were partners in the SPG Lube business, I was the one who ordered our lead in from a foundry. The first ton we split was 1-30. A while later I ordered another ton but this time specified 1-20. However, I forgot to tell Garbe. Some time later at a match he was telling someone that he was shooting 1-30, and I took him aside and corrected him. The point is that a shooter of Steve's quality hadn't been able to tell the difference. And that's because there's not much.
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Lee Stone
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Hmmmm. Makes me wonder what my 30 to 1 will turn into (If I had the "Philosopher's Stone" I KNOW what it would turn into. 
)
Think I'll get out my lead hardness testers, calibrate them against each other and make up some fresh bullets then let them set for a spell and test them again.
Also, does melting the alloy start this process all over again from square one? Say I mix some 30 to 1 alloy and pour it into 1 pound ingots then store it for a while. Will the ingots lose hardness or would there be a difference because of the increase in mass of the ingots as opposed to cast bullets? If the ingots do lose hardness, and I then melt the ingots, cast bullets will the bullets be the usual hardness for 30 to 1 or will they be the "new reduced" hardness?
Boy, what I do not know about metalurgy would fill a library. What I do know could probably be inscribed on the head of a pin in bold type.
) Think I'll get out my lead hardness testers, calibrate them against each other and make up some fresh bullets then let them set for a spell and test them again.
Also, does melting the alloy start this process all over again from square one? Say I mix some 30 to 1 alloy and pour it into 1 pound ingots then store it for a while. Will the ingots lose hardness or would there be a difference because of the increase in mass of the ingots as opposed to cast bullets? If the ingots do lose hardness, and I then melt the ingots, cast bullets will the bullets be the usual hardness for 30 to 1 or will they be the "new reduced" hardness?
Boy, what I do not know about metalurgy would fill a library. What I do know could probably be inscribed on the head of a pin in bold type.
Lee Stone
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kamotz
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Would it, or would it not be more important to strive for a given weight with a given lead/tin ratio? If I know my bullets weigh 540grs. with 30-1,should I risk changing weight to maintain a certain brinnell hardness? I would just want to choose the lesser of the two evils.Preferably the perishable one.Is there a metalergist in the house? who knows of a curing formula ?
Once you shoot black, youll never go back
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Michael Rix
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MLV, That story pretty well hits the nail on the head.
In my experience, a load combo that works well with one alloy will do well with the other common BPCR alloys we use, most of the time anyway. There appears to be a range or a window of pressure/bullet hardness that works well together. I have found this true whether I was loading for BP cartridges or higher pressure modern smokeless cases with cast at much higher pressure and velocity.
Mike T., I believe when you are asking “does 20:1 turn into 30:1” you are wondering when does the hardness of a bullet cast from 20/1 soften to the point that equals freshly cast 30/1? Storage temperature and exact metal makeup will vary the timeline somewhat but the answer for pure metal at room temperature appears to be about ten days to two weeks. Remember, this change is so slight that it is not really meaningful as applied to what we are doing.
I do not have a complete chart of all the lead/tin alloys I listed extended out to the point of no meaningful softening. That would be fun to have and add to the understanding but does not change anything. We already know these alloys work well, even after months of storage.
If I have to invent a case where it would be a problem it might go like this. You work up a very hot load (for BP) that develops pressures on the higher end, again keeping in mind we are talking BP. And then seat a freshly cast bullet made from one of the softest alloys like 50/1 that is to be used for your once in a lifetime elk hunt. You have worked up your load ahead of time. Then three months later when you arrive at the camp and the skeptical outfitter gets a good look at your singleshot rifle with iron sights and BP load, he says. “Some of the shots you might get could be a little longer than fifty yards. How about you let me see you shoot that thing and see how it (you) does.” Now three months old, the cast bullets that worked OK before MIGHT have softened to a point outside the pressure window. Maybe the signs of this are leading, (no big deal in a hunting load) nose slumping and or just plain wild shooting. Remember, this is just a story. Most likely the soft bullets would work just fine even softer and you would get your elk, show the outfitter a thing or two and be the hero with your friends.
Lee, Each time the metal is melted the clock starts over again. I don’t know if large masses of alloy, as in a pig change at a different rate however the more I think about it, it must be the same for all sizes and amounts, as I don’t recall reading any specific weight or size linked to this.
Kamotz, just my opinion, this is not worth worrying about. Cast good bullets with the alloy you have and don’t worry about the weight, batch to batch. If with in the batch the weights are close and the bullets look good, shoot them. They will go where we point them. The big trick is in the pointing.
Michael Rix
In my experience, a load combo that works well with one alloy will do well with the other common BPCR alloys we use, most of the time anyway. There appears to be a range or a window of pressure/bullet hardness that works well together. I have found this true whether I was loading for BP cartridges or higher pressure modern smokeless cases with cast at much higher pressure and velocity.
Mike T., I believe when you are asking “does 20:1 turn into 30:1” you are wondering when does the hardness of a bullet cast from 20/1 soften to the point that equals freshly cast 30/1? Storage temperature and exact metal makeup will vary the timeline somewhat but the answer for pure metal at room temperature appears to be about ten days to two weeks. Remember, this change is so slight that it is not really meaningful as applied to what we are doing.
I do not have a complete chart of all the lead/tin alloys I listed extended out to the point of no meaningful softening. That would be fun to have and add to the understanding but does not change anything. We already know these alloys work well, even after months of storage.
If I have to invent a case where it would be a problem it might go like this. You work up a very hot load (for BP) that develops pressures on the higher end, again keeping in mind we are talking BP. And then seat a freshly cast bullet made from one of the softest alloys like 50/1 that is to be used for your once in a lifetime elk hunt. You have worked up your load ahead of time. Then three months later when you arrive at the camp and the skeptical outfitter gets a good look at your singleshot rifle with iron sights and BP load, he says. “Some of the shots you might get could be a little longer than fifty yards. How about you let me see you shoot that thing and see how it (you) does.” Now three months old, the cast bullets that worked OK before MIGHT have softened to a point outside the pressure window. Maybe the signs of this are leading, (no big deal in a hunting load) nose slumping and or just plain wild shooting. Remember, this is just a story. Most likely the soft bullets would work just fine even softer and you would get your elk, show the outfitter a thing or two and be the hero with your friends.
Lee, Each time the metal is melted the clock starts over again. I don’t know if large masses of alloy, as in a pig change at a different rate however the more I think about it, it must be the same for all sizes and amounts, as I don’t recall reading any specific weight or size linked to this.
Kamotz, just my opinion, this is not worth worrying about. Cast good bullets with the alloy you have and don’t worry about the weight, batch to batch. If with in the batch the weights are close and the bullets look good, shoot them. They will go where we point them. The big trick is in the pointing.
Michael Rix
"Vegetarian" Old Indian word meaning lousy hunter.
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JAGG
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I shoot mostly trapdoor springfields with BP ! I have tried the 1 to 40 ,30 25, 22. and didn't get any accurasy until 1 to 20 was tried ! Wheel weights or any mix with antimony in it would be all over the paper ! My grooves are about .460 and bores .450 ! Groove size .460 bullets still shot lousy with antimony mixes and wheel weights , same for hollow base bullets loaded to 70grains 2fg made with WW's ! My bores are like new except for one and that one will give me 3 shot clover leafs groups with heavy hunting loads , with 1 to 20 only ,but not with hard antimony containing alloys ! Even tried 3fg heavy loads with WW and still they just wouldn't bump up and shot worse ! My findings over the years ! This may have to do with chamber sizes also ! JAGG
JAGG