I was reading their text which said:"The .358 Norma is a short magnum and it fires a 250 grain bullet at 2,576 fps."

This is not quite correct, imho. When I had a BRNO .358 Norma mag, the ballistics it claimed in Normal factory ammo was a 250gr. at 2,7++fps.
I just did a search and found this, for Norma 250gr Oryx. load: 2756 f/s 4217 ft.-lb

A .35 Whelen loaded to 65,000PSI will do 2,576fps with a 250gr., just as will a .338 Whelen do 2,550fps.

Just looking at the numbers, and it appears WR got the numbers correct, just not in the right order.

Quite a rifle!!!