onondaga
posted this
02 January 2014
http://www.castbulletassoc.org/view_user.php?id=1738>GBertolet :
It is not just antimony as Rick and Duane have said. The thermodynamics Rick mentions is very important too but the addition of Tin is specific to lead bullets alloys as a wetting agent to increase fill out flow quality in the mold when casting. 1.5% Tin is the minimum addition to significantly increase fill out and flow cast-ability. Higher amounts do increase this quality to a point .
I am a retired casting analyst and have answered this casting question thousands of times in my career. I worked as a casting instructor and technical consultant for a Dental alloy refining Co. many years. The answer is the same for bullet alloys as it is gold precious , semi precious and non precious dental casting alloys. The flow enhancing elements are different with Dental alloys and the thermodynamics are higher in temperature, but the principals are equal.
Yes, thermodynamics controls casting size to a significant degree, I can readily control bullet diameter about .001 to .003” with casting cadence to warm mold temperature and increase bullet diameter. Pot temperature has a lesser degree of effect in that a hotter pot temperature has minimal effect on increasing bullet size if the casting cadence is not fast enough to raise and maintain a higher mold temperature..
Getting the thermodynamics Rich mentions to get slightly overall frosty bullets is not easy and adding gentile cooling he mentions will make larger bullets than shiny looking bullets from a cooler mold and a cooler alloy pour. Thermodynamics have a higher degree of effect on bullet size than Antimony does. None the less, Antimony is a helper for increasing bullet size from a given mold.
How many times a minute are you dropping bullets from your mold????
How many cavities in your mold???
Do you have an accurate pot thermometer????
Do you check bullet quality between pours????
Do you dump sprues back in your pot during a casting session????
Do you already have 1.5% tin in your alloy????
Are you ladle pouring or bottom pouring???
How long is the stream of metal flow to your sprue gate hole for either type of pouring????
How big are your sprue puddles on the top plate of your mold when you pour????
Your answers to these questions control your bullet size.
This gold casting, lower right is 3,000 years old and from an archaeological dig in Israel. Thermodynamics for mold fill-out is nothing new and the science is well defined:
http://s30.photobucket.com/user/rhymeswithwhat/media/Israel3000old_zps9eaece5b.jpg.html>
 of that bullet composed of?</p>
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