Is this too simple?

[condorjohn]

If I take 1 pound of pure lead, 5 BHN, and 1 pound of an alloy known to be 15 BHN
and mix them, will I have an alloy at 10 BHN?

If this is a dumb question, just send me to my room...

Condorjohn

[bumpo628]

While it is not that simple, your estimate is actually not that far off. For example, Lyman #2 has a hardness of 15 and when mixed with pure lead 1:1, it has an estimated hardness of 11.6. I checked a couple of other examples and the estimated values were typically just over the average too. See the formula below that I used; it came from Rotometals.com

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.
Brinell = 8.60 + ( 0.29 * Tin ) + ( 0.92 * Antimony )

By the way, the formula never seems to calculate the correct hardness according to the tables either, so there is only one real way to find out - mix, cast, and test.

[sqlbullet]

As bumpo mentions, BHN is not a linear scale. This is made even more complicated by the fact that your BHN 15 alloy is almost certainly a ternary (three part, lead, tin, antimony) alloy, perhaps including grain refiners in trace quantities such as arsenic or copper.

If you know the composition of the alloys you are mixing, then you can calculate the resulting composition, and then get a good idea from a chart the probably BHN. However, hardness can be affected several points in an alloy containing tin and antimony by the temp of the lead at casting time, and the ambient air temperature of the room where it was cast (if air cooled).

This leads us back to the primary advice given. Mix a little and test under your casting conditions and see what you have.

As an aside, let me offer one final piece of advice that many here far more sage than I will echo. Don't be so concerned about BHN. Worry about fit first. Dead soft lead will shoot find in most handgun loads as long as it is properly fit. If you have specific problems with leading or accuracy, bring the problem here with the facts, like fit, load, gun, lead alloy, etc. Then we may suggest harder, or softer, or this or that. I have wasted a lot of time solving problems before I had them, and finally learned that most of the problems I solved never were going to occur.

[condorjohn]

I guess I'm on the BHN kick because I've read the LEE Second Manual pertaning to cast boolit
shooting and the difference between FPS and pressure.
I guess I'm going to have to pay more attention it fit. as sglbullet says.
I'm not new to casting but only for muzzleloaders and that's simple... Pure Lead !
I have a Savage 340 in 30-30 and want to get it shootin'n cast...