Ron, with all due respect I wonder how you know this?
You may be right or wrong, I wouldn't know since I take your word at face value.
I would tend to understand how direct flame would affect the color of the iron or steel since the flame temperature can't be controlled as easily as with molten lead.
But not sure how or how much the heat from molten lead would alter the color.
And if it did alter the color wouldn't it be only a little bit on the surface?
Perhaps easily dealt with?
I will admit that using molten lead could be taking a risk.
I wouldn't know where to research the answer to the question of how much risk of damage can molten lead cause to an antique barrel, or antique barrel exterior finish.
Here's the photo of the barrel: --->>>
http://castboolits.gunloads.com/atta...3&d=1608459635