The late gun writer Elmer Keith, who learned to load cap and ball revolvers from Civil War veterans about 1912, wrote in his book, Sixguns:
"I had one .36 Navy Colt that had a pitted barrel, but ... it would cut clover leaves for its six shots at 20 yards, all day ..."
My 2nd generation Colt 1851 Navy isn't quite that good, but at 25 yards from a benchrest it will put six balls into a 2-1/2 circle if I take the time to load it carefully.
My Uberti-made Remington .44 will put six balls into 1-1/2 inch circle at 25 yards, from a benchrest.
I've done this with both guns numerous times, so it's no fluke.
But in the end, it must be remembered that each gun -- old or modern -- is an individual and some shoot better than others.