Look at all those beautiful cast bullets. Almost like little soldiers standing in formation. Unfortunately, there are a couple additional steps that are necessary after casting and before seating those bullets into primed, charged cases:
Bullets come out of the mold slightly oversized and need to be squeezed down to the desired diameter.
And while we call it ‘lube’, it’s main purpose is to act as a gas seal while the bullet travels down the barrel. With out that seal, the hot combustion gasses would sneak up alongside the bullet and welt some of the lead, depositing it on the barrel wall. Lube Good. Leading Bad.
If you are interesting in delving into bullet lubes a little more, or maybe even contemplating making your own, here is a great article.