John Buhmiller opined that in order to get decent accuracy out of .458 WM cartridges fired in a .450 Watts chamber, the twist needed to be reduced to something like 22 inches.

My Watts, on a pre-64 Winchester Model 70 action, has a 22 inch twist and digests .458 WM ammunition with no ill effects. My Watts also has a recoil lug on the barrel, and the stock has withstood a great many full loads (but no 600 grain Barnes loads).