I was asked earlier today about bullet alloys 20/1 specifically. When the alloy is molten do the lead and tin separate over time? My answer was I don' think so but I thought I would ask. Thanks.

Tin separates from lead. Tin is lighter than lead so it floats to the top.  Farmer logic.

Schutzenbob wrote on Mar 24^th, 2025 at 1:19am:


Separation:

BOB is right -- there won’t be any phase separation.

CHRIS

Tin and lead alloys do not separate once the full alloy melting temperature is reached.
However light impurities like zinc that do not form in the alloy do separate and float to the surface at the full eutectic alloy melting temperature.
I do not flux to drive these impurities back into the alloy.
I scoop them off.
Lead-tin alloys, have melting points lower than either pure tin (232°C) or pure lead (327°C).   
A eutectic alloy of 63% tin and 37% lead melts and freezes at a single temperature of 183°C (361°F). 
Here's a more detailed breakdown:
Pure Tin: Melts at 232°C (450°F). 
Pure Lead: Melts at 327°C (621°F). 
Eutectic Tin-Lead Alloy (63% Sn / 37% Pb): Melts and freezes at 183°C (361°F). 
60/40 Tin-Lead Alloy: Melts in a range starting around 188°C (370°F) and becomes fully liquid at 375.8°F. 
Other Tin-Lead Alloys: The melting point of tin-lead alloys varies depending on the tin and lead percentages. 
Lead-free solder: melts at about 220°C 

"I do not flux to drive these impurities back into the alloy.
I scoop them off."

Very interesting comment.  I'm not a "Master Caster", but have been doing it a long time.  When I started BPRC shooting several years ago, I was fluxing my melt like most places suggest.  My alloy was certified 20:1.
I was getting occasional flaws in the castings from what appeared to be impurities in the alloy melt.
For some reason, I neglected to flux a melt and noticed an absence of impurity flaws. Stopped fluxing and this has not been a problem.  I guess the fluxing need is dependent on the alloy mix and the purity of the metals?
Thanks, Dave!
Mike.

I cast in a similar manner to Jeff except i return the skimmings to the pot after the end of the casting session and flux as the first step.  I don't shoot in as cast order but I do weigh them in that order.  I preheat my moulds on a single burner cook top and usually only have 10 bullets or so that weigh less than my target weight.  I keep these for practice. I sort by weight in .1gr increments and the last bullets cast in a session typically weigh the same as the 15th or 20th ones. Out of 1000 bullets that I cast from my 3 groove spitzer Darr designed mould, The sorted bullets are all within .5 grain of each other.  While I don't buy virgin lead, I have relied on soft lead flashing from a local scrap yard.  Unfortunately they went out of business.  I did buy 300+ lbs of unused flashing and cast billets from Bob Zimmerman's estate that should keep me going for a few more years.  I do use pure tin.  The last bullets I

Jack

Most of the flashing that I got for $1 a pound from the recycler had a lot of the tar removed, but melting it was still nasty. I would not flux it at all. If I had time I could ask the guy who was in charge of lead to separate out unused trimmings. He needed 2 months heads up to accumulate 200 lbs but it was worth it. I always slipped him a 6 pack of beer for his trouble. None of the local recycling outlets sell lead any longer.  Someday I will probably have to make the trip to Seattle to but some virgin products.

Good conversation about lead mixtures