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heat treated wheelweight: BHN changes over time

Posted: Sat Feb 16, 2008 8:58 pm
by mtngun
There is a reason they call this "age hardening." Because the hardness changes with age.

It is hard to find age data for every conceivable bullet alloy, and it takes a long time to collect data -- every time I start an age experiment, I end up forgetting about it and eventually misplacing the sample bullets. Perhaps the age test could be accelerated by storing the sample bullets in an oven at say, 250°, to see how quickly various alloys anneal compared to WW.

Here is one of those age tests that I started and never finished. I was using my reloading press BHN tester which seems to read a little high, and straight WW, oven treated.

2 hours -- 22 BHN

1 month -- 27 - 33 BHN

2 months -- 34 BHN

3 months -- 31 BHN

4 months -- 33 BHN

6 months -- 28 BHN

9 months -- 19 BHN

12 years -- 14 BHN (old box of loaded ammunition)

air-cooled WW - 12 BHN

The burning question is, does HTWW eventually revert to 8 - 12 BHN, or does it stabilize at 18 - 21 BHN, as some people claim?

I don't know. I have heard and seen conflicting results.

Here is an age chart from the 9th edition of the ASM HT book (I think). Unfortunately, it only goes out to one year, and it is confusing to read because the time scale is logarithmic and the hardness scale is in Vickers units, but it shows the general trends. What they call alloy 415A would be similar to our humble wheelweight;

Re: heat treated wheelweight: BHN changes over time

Posted: Thu Feb 21, 2008 7:26 pm
by mtngun
I have quite a few cast bullets that are at least 3 years old.These were bought from various companies before I got into casting my own.
I used a Cabintree hardness tester on these.

BRP-----------------335gr WFNGC- BHN 23-24
Leadhead-----------355gr WFNGC-BHN 23-24
Cast Performance-375gr WFNGC- BHN 22
Beartooth ----------375gr WFNGC-BHN 23-24
These are stored in a Mini fridge in a back bedroom,.the fridge is NOT turned on.
So this a controlled enviroment (temps do not fluctuate much )
Temp range-- 65 F -85 F, I doubt it gets to 85.
I am sure LH,.CP and BT heat treat there bullets I am not sure about BRP,as to why I have not seen a drop in BHN?,could be enviroment,I checked my tester against a semi known standard (BHN 12) of my NEWLY cast WW bullets and the tester came out at BHN 12 so there is no problem with the tester.I have read other articles and books about the BHN dropping over time I have not seen it though in the bullets I have.
I quess I can try again next year :?:

Re: heat treated wheelweight: BHN changes over time

Posted: Thu Feb 21, 2008 7:28 pm
by mtngun
I scrounged up some old bullets and tested the hardness.

-- approximately 15 years old, probably oven treated WW (the box wasn't labeled but that's the way I remember it :roll: ) 24 - 26 BHN

-- 11 months old, oven treated mystery alloy (probably WW + some tin, range scrap, etc.) : 24 - 28 BHN

And here's some data from my notes. These are not the same bullets. :

-- 9 month old oven treated WW : 19 BHN

-- 18 month old oven treated WW : 16 BHN

-- 12 year old oven treated WW : 14 BHN

I don't why the hardness varies so much.