BHN calculations

[KenH]

Hello all, there have been several lead alloy calculators I've found are based on the formula found at bottom of page:

http://www.rotometals.com/Bullet-Casting-Alloys-s/5.htm

where they say:

"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."


and use formula: BHM = 8.6 + (.29*%Tin) + (.92*%Antinomy)

The problem I see with this formula it does not allow calculation of any value less than 8.6 BHN, even for pure lead. Also, if you check RotoMetals BHN values for their 40-1, 30-1, 25-1, and 20-1 alloy mixes it looks like they just used the above formula.

By the statement each 1% addition of Tin increases hardness 0.3 units.... Then if you add 3% Tin to pure lead (gives a 30-1 mix) the result should be 5.9 BHN? Yet, RotoMetals say their 30-1 mix with 3% Tin has a BHN of 9.

Has anyone with ability to measure BHN tested their 40-1 mix for hardness to compare to RotoMetals values? Their values just don't add up to their statements.

Please understand everyone, I'm very new to this level of mixing alloy and am looking to learn and understand.

Ken H>

[bangerjim]

Do NOT get lost in the weeds on BHN! If it is 8 or lower.......don't worry about it. Call it pure. And to not sweat the math. Just use the calculator. And no, the calc will not give you 5 for pure lead......we already know it is 5 and are not mixing for it. That is where the fudge factor is.....in the bottom end.

The FREE calculator spreadsheet on here is good....and quite accurate. I use is every time I mix. It comes very close to my Cabine hardness tester every single time.

The calculator is wise. The calculator is good. Just use it and trust what you get. We do.

BHN is not that critical these days. FIT IS KING, not hardness.

[KenH]

Thanks for the input Jim - and I'm not so worried about exactly weather the BHN is 6 or 7 - either is just fine. What I'm trying to resolve is the math. Math is an "exact" science and the math doesn't add up with the normal formula for values less than about 9 or 10. I like it when the math adds up:) :D

"IF" the math isn't going to calculate properly below 9, there should be a great big caution to avoid below 9 or 10 BHN calculations.

Ken H>

[bangerjim]

That is what happens when a simple topic like hardness is over "thunk". [smilie=s:

Why are you calculating the hardness of "pure" lead......<9????? I, as most, are more concerned about the accuracy of the math at 10-18. What are you "mixing" in the 5-8 range that you are so concerned about???????

You must be an engineering-related person, as I am. I am a perfectionist in all that I do. But I really do not let math formulas get in my way of fun with this hobby when it comes to alloy mixes. I just use the spreadsheet which has proven very accurate for anything over 9. Below that, it gets a bit squirrelly. Bumpo, the author of the calculator, can expound in great detail about the math he used and deviations behind the formulas used. PM him.

Hardness is not that critical. Unlike being able to measure your loads to 0.1gn repeatably and accurately.

If my boolits are 9 or 10 or 11 or 12........I really do not care. I use PC on everything. And again I am not concerned if my mix lead is 5 or 6 or 7. It is close enough to get me to where I need to be. With PC, I do not loose sleep anymore worrying about hardness variations or super-hard alloys. I use a range of 9-15 for just about everything.

No warning needed from my viewpoint. Just use common sense, cast away, and have fun.

banger

[montana_charlie]

The problem I see with this formula it does not allow calculation of any value less than 8.6 BHN, even for pure lead. Also, if you check RotoMetals BHN values for their 40-1, 30-1, 25-1, and 20-1 alloy mixes it looks like they just used the above formula.

By the statement each 1% addition of Tin increases hardness 0.3 units.... Then if you add 3% Tin to pure lead (gives a 30-1 mix) the result should be 5.9 BHN? Yet, RotoMetals say their 30-1 mix with 3% Tin has a BHN of 9.

Has anyone with ability to measure BHN tested their 40-1 mix for hardness to compare to RotoMetals values? Their values just don't add up to their statements.
I have not ever tested 40-1, but I have tested 20-1.

Rotometals (and all of the ancient charts) will say that 20-1 has a BHN of 10.
Testing 20-1 with a Cabine Tree tester will also lead you to a result of 10.

The actual number for 20-1 is 7.8 BHN.

The following list was put up by (the late) Dan Theodore, an accomplished experimentor who left very little to chance.

Certified Lead: 4.5
Certified Tin: 5.0
Certified 20-1: 7.8
Certified 16-1: 8.2
Certified Lyman # 2: 15.4

When properly used, the Lee tester will return these values.

[KenH]

Thank you Sir - that is the info I was looking for. I was planning to very carefully mix up some 40-1 & 30-1 to test with pencils which is the best I've got for testing - and they do work pretty darn good. BUT - your info takes care of that.

Interesting with Tin = 5 BHN and lead = 4.5 BHN, they can be alloyed to a good bit harder than either lead or tin. That's what makes alloying so interesting.

I think RotoMetals (and other places) just use the standard formula with the factor of 8.6 without taking into consideration that prevents the formula from working with lower BHN values.

Thank you for your input.

Ken H>

[KenH]

Banger: I've just started PC'ing some lead also - still amazed how well it works. Using Harbor Freight Red and it just doesn't look right for bullets :D I'm thinking of ordering some of Smoke's clear PC - that should allow my bullets to look like bullets :)

Do you size for groove diameter with PC'd bullets? OR - a tad over? Under groove?

Ken H>

[bangerjim]

I try for 0.002 over. Sometimes it is not possible with the dies available.

The only version of boolit I do not like with red PC is that 200gn RN mold Lee makes for 45LC. When loaded, they look like little tiny red lipstick tubes!

I coat every color on the color wheel! Just mix, spray or tumble, bake and get oooohs and aaaahs at the ranges! Everybody has seen plain old silver lead boolits before. Not bloody Zombie green or Hershey's chocolate brown or Dark Bing Cherry red.

banger

[KenH]

Yea, the wife said that about some 50-70 loads I did with the red PC - "looks like lipstick" she says.

[Nueces]

Formulas like that quoted by the OP are just linear fits to a part of the hardness curve. Starting at pure lead, this curve is relatively more flat, then it steepens and can be approximated by a line (or plane) for a useful range of percentages of tin and antimony. If the formula curve is overlain with the measured hardness curve, you can see that it fits pretty good above bhn = 8.6 and diverges below that.

[KenH]

You are absolutely correct on the formula, and I really appreciate Bumpo628's work. His spreadsheet is what got me interested in the whole alloying of lead. The engineer in me wants the math to work out correctly, OR - have a note saying the limits of the formula, just as you mentioned above. Also, a note should be made that ONLY tin and antimony percentages are used in calculations.

Bumpo's spreadsheet sure started me on research which has taught me a LOTS more than I ever considered about alloying.

Ken H>

[Spector]

My engineering background plagued me for many years. At 68 years of age I have found life is happier if I don't worry about the ''why of it'' so much and just utilize what others have figured out and been kind enough to share with us.

The more hard fast rules I believed and followed led me to a pretty rigid life. After my wife died I discovered the rudder had fallen of my ship and I'd lost all my navigation charts. No longer a point ''A'' to point''B'' guy I'm learning to just enjoy the journey.

I found that reinventing the wheel gets tiresome, for those who seem to have a choice in the matter. And then someone like Gaston Glock comes along and I just have to grin.....Mike

[Nose Dive]

I believe BANGERJIM is dead on....

I too am not too sharp on my 'gozintas'.... all the charts,,, calculators... figgeruing.... cyphering.... by me buddy....

I 'trash out' in my smelt pot and call it 'pure'..... them mix 75% pure and 25% some WW's...bit of pewter or tin or solder....

This is MY ALLOY for all my pistolies..... 45...10mm...38.... 'slug' the barrel.... 001 or so over bore as a boolit.... go for it....

I water drop....age about 90 or 100 days or so...size...lube...load....shoot... no leading...good accurcay ...

KISS.... keep it simple stupid.... "stupid' for me!

Nose Dive

Cheap, Fast, Good. Kindly pick two.

[KenH]

Oh, I agree with all ya'll say as far as "does it really matter" what the BHN number is as long as it shoots good. I shot thousands of cast bullets back in '70's when the idea was "harder is better" so I cast pure linotype with good results. From what I remember (memories are fuzzy) the best accuracy was around 1700-1800 fps (no chrono back then in stone age) :D using Alox lube which was by far the best lube for accuracy. Even in those days I wasn't interested in high fps numbers, but in accuracy.

My interest was in if there's math formula, it should work, or be stated under what conditions it will work.

Ken H>