I have been shooting unpatched round balls in my rifle for years ,
but I use an oversized ball that fills the grooves ans "seals" the rifling
if there was a gap between the bottom of the rifling and the ball, the gasses running through this space could erode the barrel, mainly at the breech (I own a rifle that was ruined that way)
Of course this will not happend with just a few shots.....but don't get used to do so
my advice would be= if ,for some reason, you have tu use a naked lead ball, be sûre to use a size large enough to avoid any leakage of gas and don't forget to grease it,, to ease the loading and to avoid lead deposit
usng a big greasy wad could help but will probably not be 100% efficient
of course, as there is no patch to push the soot, the barrel should be quickly cleaned between the shots, just before loadind the bullet
sorry for the spelling, English is no really my cup of tea, just trying to help