Bullet Hardness
Posted: Sat Feb 07, 2004 11:34 pm
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
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