There are several schools of thought. The big problem is enough Aspirin to control the pain from multiple thoughts, as if one (thought) weren't bad enough. I frequently get into friendly discussions with "others" whom champion the notion that bullets "bump up" after passing through restrictive cylinder throats. I am of the opine, Once a bullet is swaged to a specific size, it (the bullet) is that size. Even more so with Ball.
I have recovered numerous fired Balls from soft medium. Balls I fired. Through my Pietta. The 451 Balls swaged down to Pietta chamber size when loaded and after being fired, the band that shows the swaging and the light land engraving, was still chamber size, so I would argue, don't count on Obturation to fill out the bore. However ....
With Cap Guns, it doesn't seem to matter a whole lot. Some guns will shoot really nice groups with 451 Ball, some guns will like 454 Balls and Rugers demand 457 Balls. The only consideration for me ... personally ... is the force required to get those really oversize balls into the chambers. I've seen lots of folks bend and break their OEM loading rods (I use an off the gun cylinder loading stand).
There is an outfit in Texas (Longhunter Shooting Supply) Whom advertise chamber reaming for their guns. If you wish max accuracy (Bulls Eye Level), they will, for a Hundred bucks per gun, ream you chambers out to 451. Whether that make a worthwhile difference, I can't personally say. EXCEPT: Past experience with Suppository Shooters would reveal a bullet sized about 001 over groove diameter will give the best accuracy and virtually no leading. YMMV. I have no desire to ream one pair of cylinders have those cylinders require 452-454 balls, and then forget which gun they are in. I have the memory of a Gnat.