Every gun is different.
There are some folks who swear by using bore size balls and tight patching which could prove to be difficult to load without using a mallet to tap the load in with.
One of the differences between barrels is the depth of the rifling and whether there is enough room in the rifling grooves to hold the excess patching.
If the ball gets swaged into the bore, it won't strip the rifling and will have maximum spin imparted on it.
With the shallower rifling of many inlines, that might not be such a bad thing, but their fast twist rates don't always produce the best accuracy.
It's possible to shoot a bare ball along with an over powder wad to help seal the gas blow by. But understand that it's just an experiment and that it may or may not be very accurate, and that it takes some courage to go forward investing in a mold to try it. I would try to find some .50 balls to try it out with first.
I think that it would work at short range with relatively light powder charges and any decent performance beyond that would be a bonus.
A .50 ball may even require a .005 patch to engage the rifling better. And experimentation would show which would be the better way to load and shoot them. A thin cloth patch would hold lube vs. a paper patch.
I've shot very loose .440 bare balls from a single shot inline .45 pistol and surprisingly they stayed on target at 25 yards. But because they were so loose in the bore, the muzzle had to be held upwards until being fired. The velocity was low [25 grains of 777 fffg] and there was no leading, but since they didn't even engage the rifling it was like firing them from a smoothbore.
Hornady has a "Hard Ball" which is a .485 hard round ball fitted with a special sabot which I think is intended for inlines. I've never heard reports about how accurate they are, but the sabot does significantly change the characteristics vs. simply shooting a round ball.

https://www.hornady.com/shop/?ps_ses...7490eba72ce09c