Does air-cooled COWW alloy take a few days for BHN to stabilize?

Ian

Notorious member
Case in point, just yesterday I tried to shoot up about 25 rounds of PC blackout that had grown too big to fit my other two blackouts. Guess what, now it wouldn't go in the fat-chambered one anymore either, so I have no choice but to pull them. These were double coated to fit the tightest one originally.

As a rule for anything other than bench loads, I make sure my bullets have some loaded clearance. They shoot better that way with the appropriate design, and I get fewer surprises a few months down the road. I have almost entirely abandoned bore-riding designs.

Ternary-alloy bullets which have aged until they are stable (how long that takes varies widely, especially if heat treated or other trace elements are present) tend to shoot better, period.
 

Rick

Moderator
Staff member
Don't know what I might be doing different but as someone that has done a tremendous amount of heat treating WW alloy and sizing before heat treating long term storage has netted very little difference in diameter. Mostly measured in tenths not thousands. I competed with heat treated CWW +2% Sn at 18 BHN, they were sized to .357", .358" sized bullets would not chamber in the FA's tight throats. Bullets heat treated and stored for months chambered fine. I don't lube the heat treated bullets until I am ready to load them when I lube in a Star with a die .001" larger than the die they were sized with. Never has the .001" larger die sized or even touched these bullets at all even after months of storage.

To answer the OP question - Does air-cooled COWW alloy take a few days for BHN to stabilize? Yes, a few days with a minimum 2% Sb. The bulk of increase in BHN will be in the first few days with minor increases in BHN for a few weeks after that. After that they will very slowly begin to age soften and probably back to original air cooled BHN for that alloy. But don't get too wrapped around the axle over that because it's not possible for you to live long enough to see it. I tested bullets of CWW +2% Sn which is 12 BHN air cooled, heat treated them to 30 BHN and after a full 10 years they were 26 BHN and still chambered in the FA.

The time curve for age hardening after heat treating is determined by the percentage of Sb, the higher the Sb percentage the faster the time curve. 2% Sb CWW will be close to final BHN within a few days. Conversely lower percentages of Sb will take longer. Will high Sb percentages (5%+) grow in diameter with long term storage? Possibly but I have never tested this. The other thing that will limit the final attainable BHN is a high percentage of Sn, again 5%+. The higher Sn percentage could also speed the age softening time curve.

I have tested enough to confirm to me that it's not bullets growing in diameter that opens up groups but rather shooting bullets of various BHN within the same group. If your bullets vary in BHN from, as an example, say 15 to 20 you can expect to see pattern's not groups at 100 yards and beyond.
 

BHuij

Active Member
Sounds like in addition to my ongoing "BHN over time" tests I should probably set up some real long-term "diameter over time" tests.
 

Rick

Moderator
Staff member
Sounds like in addition to my ongoing "BHN over time" tests I should probably set up some real long-term "diameter over time" tests.

Be sure to keep accurate and complete notes, include date, Sb%, Sn%, heat treat temp and duration, storage conditions such as unheated in winter etc.
 

BHuij

Active Member
Short of a mass spectrometer, how does one accurately determine the exact composition of an alloy? I'm just using COWW alloy, which means all my results (and I will share them) will be somewhat generalizable to other people's COWW alloy, but not perfectly so. And while I can estimate Sb and Sn % based on stable BHN after air cooling, I don't really know for sure. Let alone things like As, Zn, and Cu content.
 
Short of a mass spectrometer, how does one accurately determine the exact composition of an alloy? I'm just using COWW alloy, which means all my results (and I will share them) will be somewhat generalizable to other people's COWW alloy, but not perfectly so. And while I can estimate Sb and Sn % based on stable BHN after air cooling, I don't really know for sure. Let alone things like As, Zn, and Cu content.


I don't think it matters a whole bunch in the end. I shoot water dropped 50/50 in just about everything I do other than subsonic 223 and 30 Badger. Even 357 at 1,000fps in my wife's 357 snubby gets 50/50 on up to well into the 2,000 - 2,500fps range with 223 for gophers and down again into the 1,200fps - 1,700fps range with 45 Colt and 454 Casull. I store my bullets unsized/unchecked(if they take a gas check) and then when I want to shoot them I size, lube and shoot them. I have found that tuning the gun for cast and making sure you have the right amount of the right lube and well formed bullets sized correctly matters more than BHN. Sometimes I cast, size and lube and shoot the same day. Other days I could be using bullets I cast a year ago. I have never known the exact content of my alloy. I know it is about 50% COWW and it is about 50% pure lead. Myself, my wife and my kids have killed a boat load of large and small game with it and we have yet to have any leading or accuracy problems once a gun is tuned for cast. I don't keep a hardness tester on hand anymore. If the gun is properly tuned and you aren't using the wrong lube or the wrong amount of the right lube you should be plenty good.

It's like that story of the engineer and the mathematician who both wanted the same woman but she told them they could only get closer to her in increments of half the current distance they were from her each time.

The mathematician walked off saying "I'd like to have her, but first I have to cover half the distance between where we are and where she is, then half of the distance that remains, then half of that distance, and so on. The series is infinite. There'll always be some finite distance between us."

The engineer stayed with a smile saying "In just a few increments I will be close enough to her to do everything I want to do".


Close is plenty good enough.
 

Rick

Moderator
Staff member
Close is plenty good enough.

That could well be right but then so is . . . It all depends on what your trying to do and what your willing to settle for and what you wish to learn by experimenting.

BHuij, a few years back over on the CB forum there was a huge test of WW alloys with samples from all over the country mailed to 3 different locations and 3 different XrF tests run on them. Quite surprising to me anyway was how consistent WW actually was. With only minor variations it was close to 2% Sb and .5% Sn with very minor percentages of basically junk that weren't enough to amount to much of any difference. Since then I've just considered my CWW as just that, 2% Sb and 1/2 percent Sn. The sample bullets I mailed in were from my (at that time) 800 pound lot of WW all blended together for one uniform lot.
 

fiver

Well-Known Member
I have a bunch of the bigger truck ones and older ones from the 70'-80's I have always considered them to be 2.5-2,75% and certainly no more than that.
 

fiver

Well-Known Member
you can blend them together into one big batch in 2 regular dutch oven type melters.
be ready to run your pile of ingots back through a process.
just run them into pot-A and transfer the melted stuff over to pot-B [both heated at the same time] then ingot them, keep slowly feeding pot-A and pouring it into pot-B.
as you dump the ingot molds from pot-B put them into separate piles.
then take 1-2 from each pile to put them away.
you'll re-blend everything a second time.
 

Brad

Benevolent Overlord and site owner
Staff member
I wish I had a large furnace to blend my alloy all together as one mix.
Do what I do.

Make batches whatever size you can. Keep the ingots from each batch in a separate pile. Do as many batches as you can/want.
Now make new piles with as even as possible number of ingots from each of the first batches. Remelting each new pile and make new ingots.
You now have as consistant as possible alloy in a large amount.
 

Rick

Moderator
Staff member
I only used one 100 pound capacity cast iron Dutch oven. Made 5 pound ingots and spent an entire afternoon re-melting the ingots from different piles. Filled it was about 80 pounds or I couldn't stir/flux. I only took out about 40 pounds and then added ingots. All of the ingots had been re-melted with all of the other ingots several times and fluxing all the while. As consistent as I could make them. Kind of a PITA until your done and there is 800 pounds of all the same alloy.
 

Ian

Notorious member
I just mark each batch I render as a "heat", and when filling my casting pot pull from all the crates in equal proportions.

One time I had too many different ww-wish batches of scrap so I sorted into 12-15 piles of ingots by batch, fired up the melting pot, and remelted an equal percentage from each pile into new batches to ensure it was all uniform.
 
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BHuij

Active Member
From my results so far, it seems like even fairly minor differences in the rate at which ternary alloys cool can have a significant impact on stable BHN at 14 days. Hence bullets quenched in room temperature vs ice water will have different BHNs. Similarly, air cooled .223 bullets cast outdoors in the winter will end up at a different BHN than air cooled 45-70 bullets cast in a garage in the summer, even if the come from the same batch of alloy.

I wonder if this accounts for the differences in COWW BHN, and people just assumed "COWW alloy isn't standardized, so yours probably just contains more Sb than mine." Wouldn't be the first myth to be perpetuated to a wide audience in the cast bullets world... *cough*RPM threshold*cough* ;)

Either way, if you say my COWW is probably 2% Sb and .5% Sn, and I can take some measures to make sure my ingots are as similar to each other as possible, that's good enough for me to temporarily cease planning my DIY Specific Gravity testing setup :D
 
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BHuij

Active Member
It's been a while, but I thought I'd share some recent test results I found interesting.

I recently did some BHN tests using heat treated and quenched 100% COWW alloy .224 bullets. This time I averaged 5 readings from bullets cast and treated in the same batches. I wanted to help smooth out measurement error by increasing the sample size, and I was interested in standard deviation. Bullets were baked at 450 F for 45 minutes before quenching in 48 degree F water.

I also did 5 "control" bullets that were not gas checked or powder coated prior to heat treating, and compared them against 5 GC'd and PC'd bullets.

14 days after heat treating and quenching, the powder coated bullets came out to an average of 26 BHN with a standard deviation of less than 1. Interestingly, the bare lead/no PC/no GC bullets came out to 27.2 BHN on all readings, with a standard deviation of 0.

So powder coating and gas checking doesn't seem to have a very significant effect on the heat treating process, provided your bullets are heat soaked long enough before quenching. It's possible it robs you of a very small amount of BHN to powder coat before treating. And although the naked bullets seemed extremely consistent, the PC'd bullets were plenty consistent enough for me after taking 14 days to stabilize.

I'm sure the experiments weren't perfect (I don't believe anyone will ever reach a true "0" SD, it's just that the Lee hardness tester only gives you 0.01" increments in dimple diameter to measure). But the results were enough for me not to worry about whether PCing is messing up my hardness goals.