If you are shootin .318 bullets in a 318 bore, for the same weight of projectile I see no reason to reduce the loads 25%. I think this stems from the lowere SAMMI pressure verses the CIP pressure due to the unsafe practice of firing .323 bullets in a .318 bore.
In Europe because the 8x57 is a popular caliber people are more used to the difference between the J and JS cartridges.

Regards