FYI, your link is to a rule book four years old (for Fullbore, not High Power Rifle - a subtle difference). Better to link directly to the NRA Rules page and let people pick the one they need so they get the current version(s).
Specifically 3.16.1(a) in the NRA High Power Rifle rules is the applicable passage I think you're looking for. Interestingly... the same line does not appear to exist in the NRA Int'l Fullbore rules for some reason.