Easy BHN Calculator?

[leadman]

I was re-reading a July 1975 American Rifleman magazine and happened upon an posting by E H Harrison to a question on mixing up alloys with specific properties.
Harrison reply was a formula to determine the end BHN when the BHN of the mixed components is known. The example aimed for a bhn of 15. The bhn of the mixed components was 20, 17.5, and 12.5. The following is the weights used to make the 15 bhn alloy.

Weight BHN
2 X 20 = 40
3.5 X 17.5 =61
4 X 12.5= 50
9.5 151

151 divided by 9.5= 16bhn The alloy actually tested 16.5 bhn

Harrison said that the alloy usually comes out a little harder than the formula indicates. The components that were mixed were in the common #1 ingots commonly used by casters rather than actually weighed.

Just thought this might be an easy method for us to mix alloys when we know the bhn but do not have another formula available. The ratios could be changed slightly if one wanted to come closer to the target bhn.

[Mike W1]

I was re-reading a July 1975 American Rifleman magazine and happened upon an posting by E H Harrison to a question on mixing up alloys with specific properties.
Harrison reply was a formula to determine the end BHN when the BHN of the mixed components is known. The example aimed for a bhn of 15. The bhn of the mixed components was 20, 17.5, and 12.5. The following is the weights used to make the 15 bhn alloy.

Weight BHN
2 X 20 = 40
3.5 X 17.5 =61
4 X 12.5= 50
9.5 151

151 divided by 9.5= 16bhn The alloy actually tested 16.5 bhn

Harrison said that the alloy usually comes out a little harder than the formula indicates. The components that were mixed were in the common #1 ingots commonly used by casters rather than actually weighed.

Just thought this might be an easy method for us to mix alloys when we know the bhn but do not have another formula available. The ratios could be changed slightly if one wanted to come closer to the target bhn.

Friend of mine did a spreadsheet for me that uses that formula so you can play around with things. It's in ounces but the relationship to pounds still works just fine. Saves a lot of paper scratching.

[bumpo628]

I think that is a handy little formula. I checked a few calcs with various tin/antimony alloys and the results were pretty close to what they should be in most cases. However, I found that the formula is less accurate when there is a significant amount of pure lead in the mix.

Example 1: 5 lbs pure + 5 lbs linotype should have given a bhn of 16 (same as hardball: 2% tin, 6% antimony), but it gave a bhn of 13.5.
-----(5 x 5) = 25
-----(5 x 22) = 110
-----(25 + 110)/10 = 135 / 10 = 13.5 bhn

Example 2: 15 lbs pure + 5 lbs linotype should have given a bhn around 12 (similar to COWW+tin: 1% tin, 3% antimony), but it gave a bhn of 9.3.
-----(15 x 5) = 75
-----(5 x 22) = 110
-----(75 + 110)/20 = 185 / 20 = 9.3 bhn

In any case, it is a heck of a lot better than guessing.
Thanks for sharing your find. I'm sure lots of people will make good use of this.

[melloairman]

I recently mixed 10 pounds of 14 bhn range lead with as close as I can guess 8 pounds of 5 bhn and went last tested at 28 days it was 9.5 bhn . I have been told that this formula is not what it should be . But in my case at this point in time it is pretty close . Marvin