'Newt' - I am not sure about the origin of your barrel, (or if the diameter was altered).

FWIW:
A Krag rifle barrel diameter would measure approx. .645" @ 24 inches from the 'closed' bolt-face.

My 1903 Springfield's barrel measures .620" diameter at the muzzle, (ahead of the front-sight band), and .647" behind the sight band.

Other clues regarding a Krag barrel are the spacing of the rear-sight screw-holes, (all U. S. Krag barrels & rear-sights use the same location and spacing), and the rendering of the 'notch' at the barrel breech for the extractor-'claw'.

Some photos that might help:

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