Zinc and Tin alloy

[arawakstorm]

Has anyone heard of mixing high-grade zinc (nearly pure) with tin to make an alloy, to make bullets? Please advise.

[I'll Make Mine]

A quick Google doesn't show any common use of zinc-tin alloys for anything other than anticorrosion plating on steel (for automotive and structural use where exposed to weather); zinc-tin alloy is much more corrosion resistant than plain zinc.

For our casting purposes, you'd probably have to melt the tin and dissolve the zinc, and cast hotter than we usually do with lead/tin/antimony alloys; the resulting boolit would be much harder and lighter than lead (probably minimum BHN around 20, and 2/3 the weight of a wheel weight or 20:1 alloy boolit cast in the same mold). It would be good practice to segregate all equipment that contacts the zinc alloy, just as you'd do if casting boolits from nearly pure zinc, to avoid contaminating lead casting alloys (lead and zinc don't play well together).

Also, as with plain zinc, best to avoid aluminum molds; zinc can act as an effective solder for aluminum.

[arawakstorm]

Dear "I'll Make Mine:

Thanks. Question....based on what I've read so far, tin seems to have a lower melting temperature than zinc. Would it be prudent to melt the zinc first, then add the tin, or should one proceed with the tin melt first? And, to "start", what do you think the tin/zinc mix should be? Just for gestalt purposes, I was thinking maybe 5% tin and 95% zinc. I also guessing that the 5%/95% mix would be based on the weight of the metals used.......

[MikeS]

arawakstorm, do you currently cast lead boolits? If not, then I would suggest you learn to cast boolits the traditional way, using lead/tin/antimony alloys before deviating and trying to cast from other alloys. There's a reason these metals have been used for well over 100 years to cast boolits.

All the folks that are terrified of lead are over estimating it's harmful effects. Or I should say they're over estimating how easy it is to be poisoned by lead. With just a few common sense precautions, such as not eating food while you have lead dust on your hands. I even had one person when I handed them a plastic bag with some lead boolits in it, practically throw the bag back at me, then ran to wash his hands! That's just silly.

[runfiverun]

tin and zinc get along just fine.
in fact zinc is used by most foundry's to pull tin from a lead alloy to refine it to pure.
i don't know how they get the antimony out.

[I'll Make Mine]

Question....based on what I've read so far, tin seems to have a lower melting temperature than zinc. Would it be prudent to melt the zinc first, then add the tin, or should one proceed with the tin melt first?

The general rule in alloying is to start with the lowest melting component, and add the others, raising temperature only as necessary to maintain a fully liquid melt. An alloy is a solution, one metal dissolving in the other; for instance, if you're making a Zamak or Kirksite alloy, you melt the zinc and then add the aluminum (and copper, for Zamak), which dissolves in the zinc at well below the melting point of aluminum (never mind copper, which melts even hotter but dissolves only slightly above the melting point of zinc). So, for zinc-tin, you'd generally melt the tin, then add the zinc (though if you're going for only 5% tin -- presumably for cost reasons -- you'll almost certainly have to raise the temperature to get all the zinc to melt/dissolve.

It might be worth looking to see if zinc and tin form a eutectic -- a word which means "best melt" and refers to a minimum melting alloy -- and if so, in what proportions. Tin and lead, for instance, form a eutectic and the alloy will melt below the melting point of either component over a fairly wide range of concentrations; you might find that tin and zinc form a similar alloy system and will allow casting at reasonable temperatures without spending all your allowance on expensive tin.

Still, it's tempting to suggest that if this worked well for bullets, it would have been done some time in the past five centuries (roughly) of bullet making, or at least during one of the wars of the past 150 or so years, wherein lead has been at a premium on occasion. Generally, lighter bullets are less desirable, and any alloy of zinc and tin will be no more than about 2/3 the density of lead (since both metals are close to that figure in pure form) -- so a 150 grain bullet mold will cast only a 100 grain bullet in zinc-tin. This is detrimental both for long range accuracy (the bullet will lose speed more rapidly, which increases both drop and drift) and for penetration (lower sectional density means the bullet is less likely to, for instance, break a bone and continue to penetrate -- an important consideration for hunting). Beyond that, hardness is an issue; if your alloy is much harder than 30 BHN, it may require redesigning the bullet to prevent overpressure from engraving rifling (or it may not; Barnes solid copper bullets don't seem to require designing in thin driving bands and such, despite the softest copper running just above 30 BHN -- the point is, you're blazing trail, which with bullet and load development may mean blowing stuff up as you learn).

[arawakstorm]

To "I'll Make Mine" and all the rest, thank you for your assistance. I'm gonna try the zinc/tin mix experiments and see what happens, and I'll keep you posted. This is fun. I'm having the time of my life!!

Thank again!

[runfiverun]

i wouldn't try the mix in a brass mold....

[I'll Make Mine]

i wouldn't try the mix in a brass mold....

No, nor an aluminum one, come to that (the only common use of zinc-tin other than plating is as solder for aluminum). Got any cast iron? Make sure they're well smoked, but if you have to, you can heat an iron mold enough to melt out a stuck boolit without hurting the mold.