Here's some pictures of revolver balls that were recovered after firing some old
anemic loads out of an Army San Marco revolver.
The ball diameters across the engraved portions (which represent the barrel lands)
measured .443, .4435, .445.
Measured from top to bottom the balls are ~.4625.
Since I didn't load them I don't know what the balls originally measured, but these show the
increase in bearing surface area and becoming slightly oblong from being swaged into the
chambers, and/or hitting the forcing cone & moving through the barrel.
I can't say if more bearing area is more or less desirable for accuracy. Every gun & make
might be different in that respect. But the reasons that most use and recommend .454's
is to prevent misfires and because some chambers are cut looser/tighter than others.
Is it necessary or desireable to use the .454 larger balls in every gun?
Who knows? Just experiment to see which ones you find to be better or worse.