This is one where I would definitely start low and work up, stopping well short of "max". A U.S. Krag rifle is one that I would never hot rod.
That said, the late Michael Petrov conducted a destruction test on a U.S. Krag once by incrementally increasing the powder charge of Bullseye powder. It wasn't until he got to an unholy amount of Bullseye - 20+ grains if memory serves - that the action finally hand grenaded. Note also that he did it with the locking lug ground entirely off the bolt, relying solely on the safety lug to lock things up.
