As far as I know, all early Krag issued ammo used a cupro-nickel bullet.  I have a box of FA from 1907 and WRA from the teens and both are cupro-nickel.  I don't remember reading anything about excessive fouling in Krags.  Of course, cleaning would have been vital since the primers used were highly corrosive, and maybe that played into reducing the Cupro-nickel fouling.