Dunno anything about RIA but yes, shotgun pellets are rated at different sizes. The sizes are determined by numbers, higher numbers = smaller pellets. Bird shot ranges in size from a 9 to a 1, depending on the game you are going after. The next bracket is then Buck where it starts at 9 down to a 1, where 1 is the largest buckshot pellet size.
Edit: Buck is a special case because the pellet size gets even larger after 1 with 00 and 000 shot. https://www.wideners.com/blog/shotgun-load-types/
Dunno where all these Conservative women are because I check all those boxes and all I find are liberals. Especially considering I live in the sticks you would think the woods would scare off the libs but I guess it attracts them because "I love to hike in the woods oh my gawd."