Raimey,
There is an "Express" proof for the 9.3x72R, shown as a crown E. This mark appears on two of my 9.3x72Rs, even though neither of them fall into the 99.7gauge designation but are close to .360. The "Express" proof is a little stronger than the normal proof, but certainly it does not make a magnum class rifle of the 9.3x72R. You may find the term "Express" applied to rifles, to cartridges, or to bullets (the Tesco style). Sometimes it is applied mainly for advertisement. Context applied to the term is more important than the term itself.
Mike