Lard maybe? How about vegetable shortening? Or a concoction using one of these?
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The only characteristic I can think of that a case lube should have is high pressure lubricity.
In the past, I have used LPS3 which is a thick brown fluid suitable for use as a chain lube.
I have also used alox2138f which is a component of nra classic bullet lubricant, certainly a high pressure application.
Alox2138f was originally used for lubricating railroad linkages and has favorable anti-corrosion properties.
I bought a lot to formulate my custom cast bullet lube. I still use it today to lube my brass before reloading.
Alox2138f has been replaced by alox350 today.
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Tomorrow, I'm going to try some fat from pork adobo. Lol.
How bad could it be?