About twenty years ago, Ross Sefreid had an article about casting Bullets from two different Alloys.
You pour enough Pure Lead into the cavity to slightly above the first driving band. You wait--this is a timed pause.
Too early, and your second allow will thoroughly mix with the Pure Lead.
Too Tardy, and the two Bullet halves won't fully fuse.
The idea is to have some very soft, expanding alloy up front--to expand; and a fairly hard alloy in back, to take the Rifling--and to Not lead the Bore.
Seyfried said that he had a measuring devise on the first pot--to precisely measure how much of the soft alloy went in.
Anyway, I've long since lost the Article. Don't remember the name of the flow measure.....
Anyway, does anyone know anything about such a process?