They may or may not work, depending upon the exact chamber dimensions of your 416 Howell.
The 416 Ruger is not based on the 404 Jeffery as is commonly believed. It is actually a new round, based on the standard magnum cartridges (7mm, 300 H&H, 300 Win Mag etc.) but without the belt.
Fired cases from my Howell are right at .5435" at the expansion ring, while those from the Ruger are .5313" with normal full power handloads.
My feeling is that the extra .012+" is slightly more than I care to deal with for this level of power. Your Call !