I don't know whose shell RST uses for 12ga, but I reload some for the old 10ga SxSs that use 2 5/8 or 2 7/8 shells. As far as I know all 10ga hulls are straight walled. Because I'm keeping pressures down, I use the same data for all my 10ga hulls - Rem, Win, or Fed. I called RST once and was asking some questions about 12ga and they said they use wads meant for tapered hulls in their straight wall hulls. He said " how else do you think we keep pressures so low "? I believe all their 12ga hulls are straight walled.
Because I like to reload at low pressures, right or wrong, I treat all straight walled hulls the same and all taper wall hulls the same. RST shells are straight walled so I'd just use data for Federal hulls. I'd have trouble believing the pressure would change more than 500 to a 1000 from a Fed to Cheddite hull, if any. If reloading at 6 to 7500psi, you won't run into trouble. JMHO