Con those velocities you mention are about what I am getting and would expect from the 416 Ruger Cartridge.

450Ackley those sure are low figures you are getting but I am wondering about that powder load you are using, seems a bit low, considering 416 remington is meant to be similar capacity. ADI list 71 grs as minimum starting load for the 416 Remington and you are 3 grns below that. I know I can get reasonable velocity from 76grs in the standard Ruger Alaskan chamber.

Comparing the load with the 416 Taylor may be a mistake as the Taylor case capacity is only 86 grs where as the 416 Ruger capacity is 95.7 grs. Thats near 10grs more capacity.

Maybe you are getting excess pressure from too light a load.