Cody:  I am sure you mean fitting a 1903 or 03-A3 'banded' front sight base and blade on your Krag.  The inside diameter of the '03 sights is smaller than the outside diameter of the shortened Krag barrel.  It is necessary to bore through the '03 base or turn-down the diameter of the muzzle end of the Krag barrel in order to fit the '03 sight on the Krag.  The top of the barrel is then 'notched' so that a cross pin holds the sight base in place on the barrel.  I believe gunsmiths use to turn-down the barrel creating a step.  The '03 sight was then slipped on and pinned into place.  The 'step down' in the barrel diameter was slight and not noticeable, once the front sight was slipped into place.  Although not "original", this sight arrangement was a practical way to provide a front sight on a sporterized Krag.  (The proper way to measure barrel length is to insert a cleaning rod in the muzzle until it comes to rest against the closed bolt.  Mark the rod, remove it and measure.  This is your barrel length).