Avoid any steel wool for removing even the lightest rust from any blued surfaces, since it will thin the bluing, no matter how careful you think you may be. A patch soaked in Kroil or any penetrating oil and placed over the area for a few hours is step 1. Next, use a piece of stiff denim or unwashed pillow ticking with more oil and rub off the remaining rust.
For rust in the chambers, I'd just use a brush with whatever solvent or oil you have on hand, then go to the range and shoot out the rest. Looks like it's light enough to have not caused any pitting or surface damage. Be sure to remove the nipples and clean all threads. I apply a light dab of ball lube on the threads before reinstalling, but some folks prefer automotive anti-seize compound. Both work well.
Years ago I got some Blue Wonder for smokeless bore cleaning. It is kinda pricey for a bore cleaner that isn't really any better than a lot of cheaper stuff, BUT it does a wonderful job of removing light rust.
Pietta and Uberti have always had a problem producing nipples of uniform diameter. #10's are my first choice to start with on a new revolver. After accumulating several cap and ball revolvers, I was able to sort all the nipples into groups to get a couple of usable sets of more uniform dimensions. If you have difficulty with your factory nipples, consider a set of Treso/Ampco nipples. I have the installed on several revolvers. They're precision made to fit #11 caps.
.454" balls are ideal. Smaller diameter may work ok, but you risk a looser fitting ball moving forward in the chamber under recoil, and possibly chainfires. A larger diameter ball will shave off more lead when seated, producing a wider flat spot around the ball called the Engagement Band. Wider the flat, the more surface area contacts the rifling, and the better potential for accuracy. This works up to the point where the ball is too big, taking too much force to seat, straining the loading lever and leading to possible breakage. .456" work well in my ROA, but are just a little too big to use in any quantity for any of my Piettas and Ubertis.
