Today, I measured the distance from the barrel crown to the front-sight base on two original U.S. Kragcarbines.
On one the distance measured .416", on the second it measured .445".
The difference (.029") is about the thickness of three 'index' cards.
The average of both measurements would be .430".
I also measured the (muzzle-crown to front-sight base) distance on five U.S. Krag rifles. Distances ranged from .429" to .439", or the thickness of one index card, (.010").
The average measurement for all rifles was .432".
This measurement is more critical on Krag rifles (than carbines) because of the need to accept and latch a bayonet.
Probably a good dimension to aim for would be .430" to .432", (muzzle to front edge of base), if attempting an original looking front sight on a U.S. Krag barrel, rifle or carbine.