Occasionally, you will see a sportered Krag with a confusing barrel.

It was an old 'gun-smithing trick' to improvise Krag replacement barrels from 1903 Springfield barrels.

Besides being smaller in diameter at certain points, a 1903 Springfield barrel may have coarse machine marks & a notch for a Springfield rear-sight /collar cross-pin, may lack rear-sight holes (for a Krag sight), may be around 23 inches long & have remains of odd lettering, and have an oddly machined extractor notch and breech-end.

Attached photos show such a barrel:

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