I've never owned a Krag with a terribly excessive bore diameter.
Most of my Krags have been model 1898 rifles and model 1899 carbines, with groove diameters running .3085" to .309".
A jacketed projectile, for .303 British, running .314" diameter (or .311" diameter), coupled with the heavier powder charge and pressure of .303 loads, as Dick Hosmer states is a needless risk.