I have found it difficult to identify with certainty, on U.S. Krags, if a surviving finish is original, an armory/arsenal refinish, or a worn armory/arsenal refinish.
(Commercial refinishes are normally pretty obvious).

I suspect most Krags have undergone trips back to Springfield Armory or other arsenals for inspection, repair, and refinishing.

I have read on several occasions about examining the interior of the magazine and looking for a "diagonal line or stain" as evidence that a Krag barreled-action was "re-blued" and incompletely dipped in a solution.

I am skeptical of this. I have not noticed this diagonal line (or I am not looking in the correct spot).

I have noticed that all my model 1898 and model 1899 Krag actions have a slight diagonal 'ridge' or corner that runs across the bottom-front of the magazine floor.
This appears to be the result of a machining operation. (This line is not present on my two model 1896 Krag actions, which I believe to be Armory 'blued/rebuilds').

Also, visible in the magazine and other protected areas, on some Krag receivers are marbled patterns of casehardened colors.

The red arrows in the first attached picture point to the diagonal 'machine mark', I have found on eight model 1898 & model 1899 actions, that I inspected during the past two days.

The top action also shows a lighter colored area from casehardening. The other attached photos show a variety of casehardened colors.

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