Zinc in small percentage in bullet alloy

[JonB]

Background:
About 4 years ago, while smelting some COWW, during the first batch of the day, I got distracted and the pot overheated, melting all the non-Iron WW's (I don't hand sort). There was a clear problem and it's when I learned of Zinc contamination and it's oatmeal appearance. I posted about that smelting session, including photos, at the other forum. There was only about 15 lbs of alloy in that batch. I have been adding a 1 lb ingot of that alloy to 15 lb pot of softish range scrap for "pistol plinker" bullets, just to use it up. I am about to do that again today, for a batch of Lee 452-228 1R for 45acp.

I got to thinking, and I remembered this:
Somewhere, on some forum? in a random conversation about alloy hardness, Ian mentions "false hardness" and then said something like this ...like when you have a small amount of Zinc in a bullet alloy. I've heard that a bullet alloy with less than 2% Zinc will cast as good as a bullet alloy with no zinc, the problems start with percentages over 2%. While I have no idea what percentage Zinc is in the alloy I'm mixing up, I'm guessing it's less than 1 percent.

Let the questions roll:
Am I remembering correctly and there is some false hardness to an alloy like this ?
And exactly what does that mean?

Trying to answer my own Question:
Is it that a hardness tester will give a 'harder' reading to a alloy with a bit of zinc compared to the similar alloy without that small percentage of zinc, but when the trigger is pulled, both alloys act/react to the same amount of pressure, the same way ?
OR
Is it, that the alloy 'IS' harder, but not any tougher ? ...and if this is the case, how is obturation effected ?

Thanks ahead of time ...for any thoughts you have to offer.
Jon

 

[Ian]

What "false hardness" gives you is toughness without the brittle. Possible to match the Brinell numbers (compressive strength only) of a naturally strong, rich alloy like linotype with an alloy like wheel weights by adding steroids to the alloy's dendrites though the process of heat manipulation and further through the combination of that and grain-refining additives like arsenic and sulphur.

Zinc is a true hardener, up to the limit you can get to stay in solution. I'm not sure how much or little zinc adds to the "false hardness" capability in a lead alloy, I never tested water-quench vs. air-quench Brinell numbers with such. "False hardness" through highly modified dendrites can have high compressive strength yet still retain a good degree of malleability and/or ductility, all good things for obturation and holding the rifling. Zinc doesn't seem to add much brittle when air-quenched, just raw compressive strength, so it must make pretty small dendrites.

Linotype has true hardness and is what it is no matter what due to being eutectic and locking the dendrites up at the freeze point like Han Solo in Carbonite. Alloy like 96/3/1 has a long mush phase and is quite dynamic even after freezing which lets a process of dendrite formation called "precipitation toughening" take place over days to months. The final structure is different from lino and part-for-part of antimony and tin, is several times more tough. Take a bullet cast from lino and an aged one cast from 96/3/1 and squeeze them in a vise: They'll both deform about the same...BUT smash with a hammer and the linotype shatters like glass while the other goes splat like chewing gum. It's all about the size and shape of the crystal lattice dendrite structure created by the alloying constituents and the shear planes formed. Maybe do a smash test vs. squeeze test with some zinced alloy and make predictions? Repeat with water-quenched samples?

 

[JonB]

I've been thinking about your suggested test.
Generally when a add a bar of Zinc contaminated alloy to a batch of kinda soft alloy, for casting plinkers, I have no way of knowing what the percentages are, making any test a BIG fat guess, which will almost mean nothing.
I do have some pure Zinc (at least as pure as the manufacturers put into Zinc WW's).
I think making up a batch of alloy with 1% Zinc into an alloy of 94-3-3 or 96-1.5-1.5 (as I have those known alloys). And then do some tests. I think the results will mean more. I could also use straight COWW's, but since Zinc likes tin, I figured a higher content would have more favorable results...for casting/fillout.

 

[Ian]

I think zinc WW are probably Zamak #3 or something. Still a good choice for experimenting.

 

[Brad]

This will be interesting to follow.

Is zinc, in small amounts, a viable hardener?

 

[JonB]

Well, I mixed up some alloy. I used 94-3-3 [as my control] and 93-3-3-1 (1% Zinc [Zamak#3 ?]).

Mixing the Zinc:
I put 9.5 lbs of 94-3-3 into the pot and set the PID for 800º and monitored it. When the temp was at 700 and the 94-3-3 was obviously melted, that's when I added the 1.60 oz wafer of Zinc. It obviously floated on the melt, I was rubbing it with a charred stick, the area where I was rubbing it, seemed to start to dissolve at about 725º just a tiny bit, but the wafer, as a whole, didn't really start melting til just over 745º and totally melted at 750º.

I'm glad I cast with the control alloy first, as when I decided to empty the pot of the 1% Zinc alloy, when it got down to the last 1/2" it was slush, it wouldn't pour through the spout, I spooned it out, best as I could, but couldn't get it all. Sooooo, I added about 17lb of pistol scrap alloy to blend with what was left, then pour those ingots...and dang still a little slush and that slush seemed to be "wetting" to the pot. Now I cast inside and upstairs bedroom and my practice is to use clean alloy and no fluxing/reducing. So, my plan tomorrow, is to bring the pot outside and fill it with some new COWW alloy and flux /reduce with a vengence.

Using a NOE mold 360-160-SWC, I cast a bunch and kept about 50 from when I got the temp and pace dialed in.
I had the PID set to 690º for the control alloy and 720º for the alloy with 1% Zinc. I did have some spout issues, the stream would all of a sudden reduce to half of what is was, using a small allen wrench to clear it, when that happened. Between that and the above mentioned 'slush', I won't be doing this full 1% Zinc alloy again. But this is still a good experiment, so I can understand an alloy, like I mentioned in the OP, and how it may work.

I checked hardness with the Lee tester
The 94-3-3 was 11.0 BHN @ 1 hour
The 93-3-3-1 was 11.4 BHN @ 1 hour
BTW, my 94-3-3 alloy, with air cooled bullets, will age harden to 16.7 BHN in a few months, according to my Lee tester and my technique, and yeah I know that is harder than 90-5-5 (lyman #2) is suppose to measure, I never really understood that, maybe I need to improve my technique?

The bullets weighed and measured the same. 160.5gr and .3600"x.3605"

I didn't water drop any, I've never tried the water drop thing and not sure how I'd setup for it, and since I've read of it's inconsistencies, I'd just use the heat treat method if I want a hard alloy. Anyway, for this experiment, I'll do a Heat treat test soon, as it didn't happen today ...that is when I'll do some Vise and hammer tests and take some photos.
Jon

 

[Brad]

Interesting. The slush at the bottom may have been zinc heavy sludge that wasn't fully mixed to the melt. As the level dropped the sludge got worse and worse.

I will be interested to see what happens with time as far as hardness goes.

One percent is a heavy contamination. A half pound of zinc wheel weights in a 50 pound melt is a bunch of zinc.

 

[Ian]

Thanks for the report, Jon. The slush can happen to anything at the very bottom since it's below the heating element. I can see it being worse with zinced alloy, but that doesn't necessarily mean it separated during the casting session.

Unless that 93-3-3 is a known quantity, I'd say it had some calcium and copper in it too. WW has all sorts of stuff in it these days that really throw the hardness numbers out the window. That's why we have hardness testers and hammers.

Just for grins, you might heat one of those zinc bullets up just to the first sign of slumping with a torch, let it air-cool for about five seconds, and tip it into a can of water. Do regular hardness tests on it for a while and see how it compares to air-cooled.

 

[JonB]

The 94-3-3 is as close to a known quantity as it gets...without the foundry certification.
I think is was Alan in Vermont ???, He has access to equipment to scan a alloy.
He does 100 lb batches of range scrap, will scan that batch, then add known solder, foundry type, and pure Pb per the alloy calculator. I've swapped for a few batches of his 94-3-3, so I have quite a bit of it, each ingot is batch color coded and matched up to a printout of the alloy calculator. I just dug out the printouts for this reply, and I see this batch also has 0.27% Cu in it and 0.00% Arsenic.

I don't think the slush was Zinc rich, but even if it was, I was casting when the pot had the near 9 to 10 lbs of alloy, that I started with, in it. Also, after I melted the Zinc wafer into the alloy (at about 750º), I did run the heat up to about 780º and added some sawdust and stirred/spooned the mix, I'm quite sure the metals were blended well. Now with that said, there was some dross that accumulated while I was finding the best temp and pace needed to make excellent bullets, I was adding back the sprues and imperfect bullets back into the melt, I obvious quit that, once I got the temp and pace right....So, that could have been a major part of that 1/2" of slush.

 

[Kevin Stenberg]

This discussion is informative an timely for me. Yesterday I was thinking about using non lead solder to put small quantities of cu into a rifle alloy. But I was concerned about the zink content of the solder. Causing problems.
After I post this. I will go to bumpo's calculator and see what I come up with for numbers. Kevin

 

[JonB]

Kevin, thanks for your comment.
It made me think about this batch of 94-3-3 alloy, since it has that 0.27% of copper, that must be why it age hardens to 16.7 BHN.

 

[Ian]

Your other clue about the copper causing the higher than expected Brinell numbers is the time (months) that it took to achieve that hardness. The effect of copper is very slow, some people reporting six months or more after casting for the precipitation hardening to stabilize. By comparison, even low-antimony alloy is usually pretty stable in a few weeks.

 

[JonB]

Tuesday afternoon, I heat treated some of each "C" and "Z"
I didn't do any hardness measuring or other testing.
I ran out of time and other projects took priority, I got called back to work.
So maybe this weekend? I'll test hardness and vice and hammer test.
Just posting this so I don't forget what day I did the heat treat.
400ºF at 60 minutes.
about 15 bullets of each (marked on bottom) all in same tuna can, dropped in cold tap water.

 

[Ian]

Cool. Work isn't all bad if you come into some money shortly after.

 

[JonB]

SMASH TEST:
9 days since Heat treat.
I used a 3 lb maul on one of each, 3 solid Whacks.
I used a large vice with gripper jaws to smash one of each, applied as much pressure as I could with one hand.

There is a tiny bit of difference in Hardness, per my testing with a Lee hardness tester.

Honestly I didn't see/feel much difference in the smash tests between alloy C and Z ...and between C-HT and Z-HT. The non-heat treated bullets smashed much flatter, in a seemingly more malleable way. As you can see in the photos, all the heat treated bullets smash tests, the bullets started to fracture.


So my conclusion is the addition of 1% zinc didn't have enough of an effect to warrant it's use.

 

[Ian]

But it doesn't look like 1% zinc had any significant drawbacks, either?

 

[williamwaco]

You guys are talking WAY over my head. I don't know the percentage but I once messed up a 20 pound pot of wheel weights. I had a full inch of silver grey oatmeal on the top. If I skimmed it off, it would reform in about 10 minutes. I stupidly tried to fix it by thinning it with more wheel weights. You all know that that didn't help. I eventually wound up with around 60 pounds of alloy with heavy oatmeal on top.

I decided to give up and toss it before I ruined any more. Just for grins, I thought, fluxing doesn't help, so lets see what happens if i don't flux and try to cast with it "as is".

Surprise, surprise, made perfectly good bullets. Over 2000 of them. They shot as good as any I have made before or sonce.

 

[RicinYakima]

You had better response than I had in the same situation. I ended up with 90 pounds that went into a sail boat keel. I could never get the bullets to fill out the driving bands or bases, even after adding 1 pound of tin to a 20 pound pot of the stuff. I tired casting from 675 to 775 degrees, measured, in a known good Ideal mould. I would even make plinking bullets.

 

[Ian]

I haven't experienced zinc contamination as "oatmeal", that's usually calcium contamination or simply an abundance of antimony oxide. When zinc is present in concentrations beyond the saturation point for the temperature, the zinc floats in a molten puddle on top like oil on water.

Williamwaco, when you say "flux", I seem to remember that you use beeswax. Beeswax is an excellent sacrificial reducant, but flux it does not and will do absolutely nothing for your zinc contamination or "oatmealed" antimony. Sawdust mixed and mashed around with the oatmeal stuff using a stick will do wonders for a variety of stuff. If you get the liquid, shiny zinc on top after a good fluxing, it can be skimmed with a spoon and gradually "frozen" out of the melt by lowering the temperature and fluxing/skimming frequently. You'll never get it all, but you'll get the excess out to the point that the alloy can be used if you cast at a slightly higher than normal temperature.

 

[Brad]

If I add much monotype I get the oatmeal dross. Takes more heat and a heap of fluxing to get it mixed in. Once mixed in it seems to remain stable and in solution. More antimony seems to cause the oatmeal like dross. It can be mixed in but it takes some work and patience.

Never had zinc. I rarely use wheel weights so that isn't a possible source.