Paint varies. So Smart Parts made a system that adapted to the paintball, not the other way around. One barrel, eight bore sizes. Buy a tiny ball: we have a .679 insert. Medium ball: be happy with the .689. Buy big or just leave paint in the sun all day: we have .695.
Stainless steel inserts are stronger and hone to a slightly smoother finish, giving you one more option in the Freak line.