Bismuth Expansion

[temard]

Bismuth has been bandied back and forth on here quite a lot on its usefulness, but one thing I notice that has not been addressed is bismuth expansion.

I'm looking to get out of using lead, and that got me onto here looking for alternatives. Bismuth alloy caught my eye, but I also noticed that supposedly, bismuth expands about 3% while cooling.

I shoot civil war reproductions with minie balls, and there isn't much space for expansion in those bullets. An Enfield is .577, and Lee molds are .575; even a hair of expansion is going to cause issues.

So how do you stop the bullet from expanding? Do you just fill the mold and then let it sit there, closed? Bismuth crystallizes, from what I understand, causing the expansion, so would keeping the mold closed until cooled prevent that from happening? I've done a bit of googling but 99% of things online about bismuth are how to get it TO expand, to make those neat crystal formations. I'm trying to get the opposite. Would alloying with tin or antimony reduce that?

Has anyone experimented with minie balls before? I don't mind doing my own homework, and I have some bismuth on the way, I'm just hoping this isn't a wild goose chase. As much as I love shooting my old rifles, I really hate how downright dangerous lead is to work with. It's a shame the best bullet material on the planet, just so happens to be a neurotoxin!

Any experiments, or educated guesses, are welcome. I'll be posting my own results when I get it cast down, I plan on casting a dozen minie balls as normal (fill mold, open mold, smack'em out), and then making another dozen with a closed mold, which is going to take forever.

[Lakehouse2012]

From what you are saying, I would treat the 3% expansion the same as how we cast oversize and the size down.

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[JonB_in_Glencoe]

temard,
welcome to the forum.

You pose a very interesting question. In my many years here, reading new posts every day, I've never seen anyone discuss bismuth expansion.
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Pro-tip: If you leave the boolits in the mold for a extended time, be sure to still cut the sprue at a reasonable time after pouring. You might want to look into the clamping (vise-grip style) handles as well as a hotplate (to preheat the mold for the next pour).
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I look forward to reading about your experiment.
Good Luck.

SNIP>>>

It's a shame the best bullet material on the planet, just so happens to be a neurotoxin!

Lead, in a un-oxidized state isn't near as dangerous as some will lead you to believe. Use proper sanitary techniques and you'll live a good long life without brain damage. Powdery Lead oxide can become airborne, so handle that very carefully...same goes with spent primers and/or cases with spent primers, whether depriming spent cases or especially important if you use dry media to tumble clean fired cases with spent primers intact.

[243winxb]

Rotometals makes Bismuth alloys. I would ask them. Bismuth & tin is $ 19 for 1 pound. Roto202F alloy.

Much info on their website. https://docs.google.com/spreadsheets/u/0/d/1RvV_oN09dk--kvApy5tXmO5LuMooLSFEqV6BCl67UiQ/pubhtml?widget=true&headers=false&pli=1#gid=0

I do not understand the chart or the alloy its for? Doesnt look like a lot of size change?

[temard]

Cheers for the replies. Responding in order:

-Lakehouse: I've only cast a few items before. Can you explain casting oversize and then size down? Especially how you'd do that with a 500gr minie ball, that thing's a monster. We're not talking 50 caliber roundballs here!

-JonB: Me too! It's actually what inspired me to log in and ask. I've gone through countless, extremely informative threads, but in none of them did anyone discuss bismuth expansion beyond mentioning that it happens, and then glossing over to the next topic.

-243: I plan to if they're open for calls tomorrow, holiday weekend and all that. I've never seen that chart, what is the context for it, where'd you find it?

[243winxb]

The chart is on Rotometal website, at the link above. Chart has to be down loaded.

As near as i can guess, the temperature makes the difference? Higher temp, more shrinkage, as alloy cools?

Dont know, my guess.

The other chart at Rotometals link.

[temard]

More expansion, if it's to be believed. Apparently bismuth expands as it cools.

I'll get back to this, ordered some bismuth/antimony/tin alloy from Roto, and I've got a brand new minie ball mold coming in for my Parker-Hale. Let's see how it shoots!

[243winxb]

Bismuth as cast diameters , may be different then pure lead? Will be interesting how your alloy/cast does?

Alloys used to regulate bullet molds.
Alloys with antimony, will make bullets larger, harder & lighter. As cast & after sizing.

Manufacturers of molds, regulate molds with their alloy. Lyman #2 is very different, compared to lee.

Lee- Our bullet mold weights for our rifle and pistol bullet molds are based in a 95% Lead / 5% Tin mixture.

Lee- .
For round ball and Muzzleloader/Conicals/REAL bullet molds, pure lead is required.

[temard]

It's certainly going to be about 16% lighter than lead, but that's not a huge issue with my particular goal of getting .58 caliber minie balls. Those monsters are already 500gr cast of lead, so even a lighter bullet is 420~gr, which is still absolutely massive.

Probably a lot more important to folks casting your standard .490 roundball.

Yeah, I've got everything in the mail now, so I'm excited to see what happens!

[jsizemore]

Here's an old thread on the subject:

https://castboolits.gunloads.com/archive/index.php/t-388299.html

I did the google thing for "casting bismuth bullets". Lots of reading. Appears that bismuth alone is very brittle. Mixed with tin the amount of expansion and brittleness is less a problem but a significant loss in bullet weight.

[dondiego]

My only experience with bismuth was with duck loads and there was NO expansion of bismuth, it just shattered! I hope that the newer bismuth alloys are better suited to cast use. I realize that the "expansion" as used here is another issue.

[Bigslug]

Final, as cast diameter is indeed a concern, but I'd also be worried about how the hollow base will behave.

My father tinkered with Rotometals bismuth/tin alloy as a possible hunting alloy for CA. We were testing for possibility of expansion ON IMPACT. Basically, we found there's two extremes - at least using water jugs as a testing medium:

1. Too high percentage of bistmuth will shatter on impact.

2. Reduce bismuth and increase tin, and you get a bullet that will stay together, but won't expand. Due to the weight reduction, downrange velocity retention suffers, but at least you can start them out a little faster. Big meplat effect would be the best choice for terminal results on game - mushrooming isn't going to happen.

How that will translate to expanding the skirt of a Minie ball I couldn't say, but I would be concerned about a too-much-bismuth slug shattering at the muzzle. Higher tin would PRRRRRROBABLY behave, but for a go-out-and-play (as opposed to hunting) option, that's going to be an EXPENSIVE projectile considering the volume of a .577 caliber missile.

I'd suggest you contemplate improving your lead handling practices, to include having your doctor check your blood for it when he's doing draws for your regular cholesterol and other chemicals. Yes, lead is toxic, but it isn't the plutonium the Dianne Feinstein camp would have you believe it is. We have numerous sep- and octo-genarians on this site who would be long dead if it were.