Sometime in the last year or so I read a magazine article on the Model 99 Savages. I am not absolutly sure, but think it was stated that older rifles of this model were not as strong as ones made in later years. Anyway, the factory pressure for a .308 or .358 Winchester cartridge may be greater than for a .300 Savage cartridge and your gun may not be as strong as those made when the Model 99 was chambered for the .358 Win cartridge. Also, I don't think the difference was in the mechanical design, but rather the type of steel used.