If it is uncapped I'd put grease in front of the balls. If it is capped you're pointing a loaded gun at something you don't intend to destroy while applying the grease.
(violates the 6th commandment of firearms safety. "Never point a gun at anything you do not intend to shoot; Avoid all horse play with a firearm".)
Lots of folks load them without wads, just using grease over the ball.
I used to always load that way, and had exactly two chain fires over the years, before using wads.
And those chain fires only involved the two adjacent cylinders, no harm done.