"35 W.C.F."
.35 Winchester Center Fire.  Typically a sign that a gun has been rechambered.  The marking is to let you know that.  Given that a Krag would have been made in .30, and it's now .35, it'd be logical to assume a barrel change. Get a .35 and see if the bullet fits in the end of the barrel. 

I'd think a Krag chambered in .35, without a barrel change, would be an interesting thing to shoot.  With a string from 300 yards away.

The first thing to do is check that bore size.