BNH recipie caculation

[Road_Clam]

Hey guys, looking for a bit of input on my BHN math for trying to determine a BHN outcome. If in theory im targeting a net BHN of 10 and I melt 2# of 12 bhn, along with 1# of 5 BHN I would add 12+12+5 = 29 , then divide by 3 which equals about 9.7 BHN. Do you agree with this math ? I have all my ingots BHN tested and separated according to BHN from my Cabin Tree tester. Im thinking this formula should get me close , then just add a bit of pure tin if needed ?

I have a lot of varied hardness, I have lead from pure (5 bhn) all the way up to 30/70 Antimony / lead nuggets.

[Mitch]

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.
For a simple equation,
Brinell = 8.60 + ( 0.29 * Tin ) + ( 0.92 * Antimony
this right from the rotometals site and the same formula the lead calculator here uses.
so if you use 8.6 not 5 for pure led you will have a bhn of 10.86

[Dusty Bannister]

Mitch, the formula provided by Rotometals does not really work when building an alloy.
Most of us use scrap soft lead, so your suggestion to change the value of lead from 5 to something else is valid. Since the OP actually knows the BHN of his "pure" lead, I would stay with that since he knows the hardness of his two metals.

Three more factors will apply. Ingots are not going to read the same as the cast bullet. Whether the alloy has reached full hardness when tested might affect your readings. Bill Ferguson tells us that the number to the right of the decimal is meaningless. Do not get lost in the details. Through his own testing, the OP will find that his figures are probably close enough to suit his needs.

Make a small batch and see if it will serve your needs. Just give things time to age harden and have fun with the hobby. The firearm will tell you if the alloy is working or not. The hardness tester will only get you to the range. Good luck. Dusty

[17nut]

The above formula works for smaller amounts of components in the alloy.

The alloy properties are not linear.

A lead tin alloy will get harder as % goes up but after @40% tin the alloy will get softer again.
The same goes for antimony, the curve will flatten out with high %.
Pure tin is @8BHN and the formula puts it around 37BHN
Pure antimony is @50BHN but the formula will put it right at 100BHN.

[bangerjim]

Use the alloy mix calculator on here for FREE. I use it all the time and it gets pretty close when checked with my Cabine tester.

I do not mix up hundreds of pounds of an alloy but keep all my "alloy elements" of the mix separate and the just add them in the casting pot on the fly. Gets me darned close to the 10-12 I cast for many guns. That way you can easily change the mix.....and makes it easy if you have to sell off some alloy in the future. I sure do not want to buy somebody else's "private" mix! Just the basic ingredients for me.

[Grmps]

http://castboolits.gunloads.com/showthread.php?t=105952

http://castboolits.gunloads.com/attachment.php?attachmentid=45784&d=1341560870

[JonB_in_Glencoe]

Road Clam,
I agree with your math...as far as math goes, but Lead-Tin-Antimony alloys don't work that way. And your 12BHN alloy may or may not have any antimony...hopefully it does.

COWW is about 12 to 13 BHN, so if your 12 BHN alloy is COWW or a very similar alloy, then I may have some good news for you.
I blend COWW 50-50 with soft lead and get a pretty good boolit alloy that will age harden to 9 or 10. 50-50 is real good for low pressure loads like 38spl or 45acp.

Since you may not know what your BHN 12 alloy is, you could blend some as you mention 2/3 to 1/3 and let it age harden for 2 weeks and see what hardness it becomes. If it is harder than 10, then you could add an amount of soft lead to adjust the percentages to 50-50.

Also, make note of what Dusty mentioned, measuring hardness of ingots may not give you the same reading as measuring boolits, since they cool at a different rate ...and I'm not sure how you make you ingots, but I will cool the ingot mold right after I pour it and it solidifies, by using a towel soaked in cold water, makes a big steam cloud...but that increases the hardness.
Good Luck.

[Mitch]

Well now i guess it is all a ballpark figure in the end.Now the question was about the math.I have found the roto formula to be close enough for the purpose of casting boolits.If you all want to get into it deep have at it.

[Road_Clam]

Thanks folks for all the feedback. My plan is for the short term to just experiment with small lots and document my findings.

[evoevil]

Good info , Thanks