7×54mm Finnish is a rare half-wildcat caliber. It was loaded by two factories, Sako and Lapua in Finland. It was designed by Lapua to be used in worn 6.5×55mm SE rifles. It's simply 6.5×55mm SE with 7mm (.285) bullet. It may be loaded with modified 6.5×55mm SE dies drilled to fit 8mm neck diameter. It was usually loaded with a lightweighted bullet.
Dimensions were measured from a cartridge loaded by Lapua and from (if two measurements) a shell that had been shot with an modified Arisaka. Because caliber is a wildcat, those can vary greatly.
In 1948, the gunsmith M. Jean Fournier sold some hunting rifles based on the MAS-36 rifle and the 7.5×54mm cartridge Mod 1929. As the French public could not use military cartridges, it was made possible in this case by reducing the caliber to 7mm, keeping the rest the same.
Should not to be confused with the 7×54mm Finnish, naming similar but cartiges are not compatible.