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Shrinkage/Expansion Factors for Different Alloys

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05 May 2021, 05:32
MCJ
Shrinkage/Expansion Factors for Different Alloys
I need to order some round ball moulds for use in a 10-bore double rifle (actually marked 11 bore, with bore diameter measured at .760"). I was wondering if anyone could help recommend what size moulds I should order based on shrinkage/expansion factors for the following two different alloys:

1) 16 parts lead : 1 part tin alloy with BHN 11 (this will be my main material)

2) 87.25% Bismuth / 0.75% Antimony / 12% tin alloy with BHN 19.3 (this is a new lead-free alloy being marketing by Rotometals for casting non-toxic projectiles)

Any suggestions from anyone? Thanks, Mark
05 May 2021, 07:28
Lamar
lead-tin alloys don't grow or shrink, nor age harden, they will eventually age soften though.

I was involved with that Bismuth alloy it's designed for hunting in California.
it don't change diameter either, and can be sized down some [.001-.0015] with no breakage issues.
it's already been used to kill a few deer and the alloy holds together with some deformation on soft tissue.
05 May 2021, 19:50
MCJ
Thanks, Lamar. Especially good to hear from someone with hands-on experience using the new Rotometals lead-free alloy. Very useful to know that that alloy can be sized down slightly with no issues, as well.
06 May 2021, 09:46
Lamar
just remember it has a pretty low melt point and you don't need to exceed that point by much to cast with it.
[but your mold still needs the heat to allow everything to operate properly.

if your gonna make shot with it, watch your melt point there too.
most shot droppers are designed to run at 700+ so you'll most likely end up switching the machine off and using a torch to keep the dripper wall hot enough to flow properly then switching it back on,,,, etc.
07 May 2021, 12:31
georgeld
By far the best is to contact Dixie.
They KNOW this stuff and will recommend
the right size for whatever patching you
plan to use.

They can make a scissor type mold exactly
what you need and won't rob you on it either.

George


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