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.