Sounds like an incorrect or modified bayonet. Can you post some pictures? Is anything else out of the ordinary with the bayonet?

Rifle barrels for all of the .30 caliber Krag barrels at the muzzle, as they were made at Springfield Armory,  were all 0.620 inches. (Except BoOF rifles.) Carbine barrels were 0.635 inches. That's why the PC and School rifles that were altered to be able to support a bayonet had the muzzle turned down slightly to fit the barrel ring/ferrule. So there should be no authentic variation on a regular Krag rifle.