Lead-free bullet casting alloy

[CZ93X62]

My 1897-made Win '73 carbine might see the hunting fields and deer woods again. I have no way to express just how happy this makes me to read.

I'll cut right to the chase--more than 2/3 of my firearms collection was disallowed from hunting usage by virtue of this "Unleaded bullets only" foofahrah. Barnes tries to service the market, but they gotta draw the line at some point--and the commonly-used calibers are Barnes' profit center. No objection to that--they aren't in business for their health. Nutbars like me that live in strange states with strange laws and customs--but who insist upon hunting and shooting with oddball calibers--that is just not a niche worth pursuing commercially. It is on us to find a way around these challenges. Ian has accomplished this, from all indications to date. I am pretty jazzed!

 

[Ian]

I think you got it from here, Allen, happy to help. Lord knows how many people have spent time and money to help me with things over the years.

I especially want to thank Lamar too, I've come to rely on his brain when undertaking off-book projects because he has an x-ray mind that sees to the heart of the issue and a way of explaining what he sees and offering solutions and predictions that almost always makes sense to me. He's also an invaluable sounding board for ideas. Take a quick read through this thread from the beginning and you'll see what I mean.

There's still a lot of ballistic testing that needs to be done (wet pack, water jugs, etc.) and I'll help as I can, but the main object of finding a lead-free alloy that can be easily substituted and shot accurately at useful velocities for hunting has, I believe, been established here in short order. I look forward to the results of others with the Sb-enhanced Rotometals alloy and hope that this turns out to be truly as useful as I think it will be.

Lastly, I'd like to thank the folks at Rotometals for making this possible by taking an interest, blending fifty bucks worth of alloy, and sending it to me gratis to test. You guys give them some business.

 

[fiver]

they almost always seem willing to help.
and they are a smaller family outfit which always gets my vote of support.

 

[CZ93X62]

Yes--Lamar's analyses and assessments are another large part of this effort. This has always been his way on the sites I have shared with him, and he has saved me some ventures down rabbit holes that would have led nowhere.

I will certainly be in contact with Rotometals shortly concerning the casting metal. It is listed on their website already, I think as non-toxic fishing sinker metal. Things like that are called CLUES where I used to work.

 

[CZ93X62]

All things considered, Mom's condition being stabilized currently--we have elected to go ahead with our trip to Seattle for Thanksgiving commencing tomorrow. I will order the 88/12/trace Sb alloy and a Lee furnace when we return, to keep the porch pirates frustrated during our absence. Kids and grandkids for 6 days will be a very fine thing indeed. And much-needed.

 

[Ian]

Enjoy your family, very glad to hear your mother is on a somewhat even keel for now.

This is what you want, not the sinker alloy: https://www.rotometals.com/lead-free-bullet-casting-alloy-88-bismuth-12-tin/ But you have to ask them to add the antimony, they blended three pounds just for me and don't stock it...yet.

 

[fiver]

Seattle? bring your rain coat we got a storm swingin in from that direction.
it'll be snow when it gets here, but yeah rain.
I know shocking... right.

 

[Ian]

Update to add, Rotometals re-blended their 88/12 batch with the .75% trace antimony addition so the alloy is available for purchase ready-to-roll. Looks like it went up a little to $15.59 currently, quite spendy but hey, it works.

During this testing I realized something. This alloy is giving every indication of shooting better than anything ever has (including jax) in two completely different rifles and calibers. If that trend were to continue, this unleaded stuff might be a really good option for the benchrest competitors.

 

[Spindrift]

This thread has been mind-blowing. Excellent, ground breaking work. Ian has
1) Recieved a totally alien metal alloy
2) Made good bullets from it
3) Done successful load development, and
4) Shot a deer with it.
.... in a couple of days. I’m pinching my arm here. Fantastic!

 

[Ian]

Finally I got a picture to focus better. The as-loaded bullets compared to being recovered frim the trap.

I ran some Quickload numbers on the unleaded loads and the .223 bullet would have seen about 14,000 PSI peak pressure after the base had moved about 2.2 inches, and only about 8,000 as the gas check was engraving the rifling. Alloy for the .22s is about 18 BHN per Lee tester, which means it should withstand about 25-26,000 PSI...but look at the bullet and you tell me alloy didn't permanently squish under pressure. Neither calculation's error could be that far off, so that leaves only the nature of the alloy's grain structure to explain the shear and deformation.

It isn't an optical illusion that the recovered .22 bullet is bent into an S. I believe that happened in the throat because a land made a deep cut in one side of the nose while the opposing land did not touch the bullet in that area at all. Notice the slump on the right side of the two middle grease grooves...I think the bullet collapsed on firing. Aside from a lot of neck clearance, the bullet had perfect support in the throat due to custom-match bullet form/size die I made, and only the gas check and 1.5 base bands were in the case neck.



The .45 Colt bullet was seeing about 11,000 psi peak pressure from the Bullseye and that peak was occurring just as the bullet base was leaving the case. Instead of collapsing, it grew from .773" to .781", measured with a micrometer from sprue cut to meplat. There appeared to be no base cupping but the whole bullet elongated from engraving the rifling. Normally (with lead alloy or jacketed lead bullets) that only happens if there are no displacement grooves and the bullet has no choice but to draw out as the lands displace metal. This Bismuth alloy appears in this instance to be drawing the whole bullet just from pressure on the bearing surfaces.

Stresses on the Bismuth alloy definitely transfer more directly than with terbary lead alloys, causing deformation and micro-fracture in some ways we are not used to seeing, though in many ways the movement (and the stresses imposed on the bullet during launch) are exactly the same.

Interestingly, the Bismuth alloy seems to transfer heat in an unusual manner too, cooling its core very, very slowly when cast into a bullet, and I have to wonder if the weirdness with cooling might be affecting the granular structure from outside to inside of the metal. Perhaps some annealing needs to be done, it should be possible to normalize the Bismuth alloy bullets after casting from what I have read.

 

[Ian]

Another pertinent read here:https://steemit.com/science/@engenu...-diagram-by-differential-scanning-calorimetry .

It gets interesting about halfway through where the author discusses the how the physical and chemical structure of the eutectic binary blend of Bi/Sn forms as it cools and how controlling the cooling rate at certain points develops finer grain structure. He also discusses coring, which is of particular concern to us bullet casters. I don't know how much of this applies to the Rorometals 88/12 alloy, or more particularly the ternary alloy I tested, but it's food for thought.

I think it may be time for me to start working on a "How-to" thread about casting bullets with this stuff.

 

[fiver]

good idea, I was concerned about getting voids because the stuff [bismuth] doesn't like to draw a sprue.

 

[Ian]

My experience with the Rotometals alloy is that it does indeed expand as it cools as people say it does, so drawing a sprue isn't the potential issue so much as different crystalline and compositional effects from outside to inside as the primary, secondary, and final phases of solidification occur.

If the mould is too warm when casting, the chewy center sweats out of the bullet for several minutes after it is dropped from the mould. Much worse thearger the caliber.

Sprue end of a .30-caliber and nose of a .45:

 

[popper]

>17% bi expands. Bi magnetic characteristic is terrible as is thermal conductivity. Wonder if As is used in Bi shot, could be a good grain refiner? 223 GC base looks like it expanded forward (BTish), drive bands don't have much tail. Sharp drive bands until shot, then rounded but grooves stayed the same. Impact swelling? Kinda backwards from all Pb based obsevances. SWAG - due to low melt temp (compression heating?), twist stress/fracture and re-solidus? Only thing I use Bi for is diverticulitis!

 

[freebullet]

Pretty wild journey.

At that alloy price point I'll keep reading but....

 

[popper]

I have a 2x 30 cal. 145gr PB mould with very small groove that you can try. Might do OK with 2x BLL.

Bi has a poor lattice structure (crumbly via very weak atomic forces) that gets held together by the Sn & Sb that act like glue (much higher atomic forces). It is a mixture, not alloy! The size of the different 'grains' interferes with the 'slip' plane. Pb is cube structure with little 'slip' resistance so it is malleable. Bi is kinda like Al, can't decide if liquid or solid around melt temp - Call it slimy. Actually Bi molecule is hard but metal has a very low BHN. Very useful as alloy additive but almost NO industrial use by itself (at this time as it doesn't really get 'alloyed' with anything). Weird stuff. Maybe this explains better. Small additives into BI don't 'alloy' but the reverse is true.

 

[fiver]

that's exactly what we were speculating the tin was going.
I was talking about maybe being able to modify the grain structure to make the lattices between the Bi molecules pack in tighter so that less Tin could be used.
it's also why I was throwing out the swage first thing, it would in effect skip the need to pack things in tighter since that would already have been accomplished and could possibly remove the effects of higher pressures before hand.
IE control some [much] of the 'skidding' and the slumping depending on the design of course.

 

[Ian]

Here's a phase diagram for the ternary but with 57% Bi. You can see why no more than 1% Sb is wanted in this mix.



Compare to the 12% Sn point on this binary Bismuth/Tin phase diagram:



So we have a sorta liquid solution above the liquid point.

The order of solidifiation, as best I can understand it without a real phase diagram for the actual alloy we're working with:

1. Somewhere above 395°F is Sb/Sn, which precipitates out of solution, "near the grain boundaries of the tin" as the temperature drops below the solid solubility point of Sb in Sn.
2. At about 395°F, Bismuth begins to crystallize into a solid, increasing the tin percentage in the remaining liquid Bi/Sn/SbSn.
3. Then, somewhere around 282°F, the remaining liquid Bi/Sn freezes. Thing is, its concentration of that liquid has changed from the original solution, so we can get coring (inner composition different from outer composition) with a much higher Sn content. This could explain the strange behavior of the bullets under stress.

 

[fiver]

what's the L?
surely they ain't using L for lead, they can't be the temps are waaay too low for that solution.

just as a comparison the tin coming out at solidification is also what happens when it exceeds the Sb in a PbSbSn solution.
except instead of finding somewhere else to go it gets trapped trying to form a new solution with the lead.

so if I'm reading this correct, it's doing it here too but it's tied with antimony [naturally] and it's pulling it along too.
that would totally back up the idea of the bullet being 'solid' [more on the solid side of the mush phase] and liquid and things are still moving.
it's like getting a mold waaay too hot and holding alloy in it until it's so frosted it won't solidify then when it does if you drop it on the table it breaks.

I think Ian's report on how he casts with this alloy is gonna bear that out.

 

[KeithB]

Does that mean Liquid + whatever element(s) listed as a solid? It looks like it they are pointing to liquidus phase change lines.