Well the REALs are very short bullets, so that's why they do well in slow twist barrels...as bullets get longer, they require more twist. A round ball is of course as short as you can get a bullet, (unless you shot a wafer I guess) so they need little twist, and, having little bearing surface a slow twist also helps to keep them from jumping the rifling.
I know that REALs shoot well in shallow groove, minnie ball rifles...I use the 440 grain (actually casts out to 456)REAL in my two minnie rifles. Have often wondered how they do in deeper groove round ball barrels.
I've always thought that if you had a good round ball barrel, one wouldn't "want" to poke any kind of slug down it, but I guess in the smaller calibers, .50" and under they could be of value to produce some additional energy. I have never shot anything with my REAL yet, but just looking at the nose shape, and the sharp shoulder tells me that they would have great "whompability".
Rat