That 255gr. load at 2,700fps very closely matches the .358 Norma Mag. factory load(250gr. 2,756fps). No flies on that load and it utilizes the case's actual capacity.

Both of my "factory" 9.3x62's & the Styer owned by the grizzly hunter from Hungary we had back in 2010 or so, measured .454" on the shoulder of a fired case, not .451" as noted above. I have 2 of his RWS (I think) factory cases he fired in camp to check sighting of his scope before he went hunting with his assigned guide.
I measured the case capacities and they match mine, at 78gr. water.