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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Attached are a couple photos of a model 1896 Krag rifle in the 64,000 serial number range.

This Krag was updated with a model 1902 sight and replacement stock, with no 'cartouche'. I am sure this is an example of the 're-blue' done on Krags at U.S. arsenals.

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Attached are a couple of photos of a model 1898 Krag rifle in the 333,000 serial # range.

FWIW - I believe this Model 1898 Krag may still have its original, but worn, case-hardened metal finish.

Red arrow shows track of machine cutter. Green arrow indicates 'case colors'.

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Does anyone know if the original factory finished krag receivers were blued or left in the natural case hardened finish?  I have read that the Springfield armory  used steam cabinets to rust blue the weapons. If this is correct for the finish on the krag those non blued areas inside the receiver would seem to indicate a dipped refinish. 

the krags went through IRAN numerous times. More times than we generally realize. Originaly the receivers were case hardened, Once case hardened it can not be done again. When the were IRAN'd they received bluing and there is indeed a spot at the inside of the lunchbox/receiver, generally diagonal, that the bluing missed, presumably because of how that part was held in the bath (my presumption). I will post a photo if my 1898 that was IRAN'd when I have a chance.

Thanks Mark! It will be interesting to see photos of your IRAN Krag.

King Carp - When first manufactured, the Krag receivers were casehardened and had a finish showing 'case colors'.

The barrels were completely manufactured separately and were 'browned' (blued) and finished, prior to being 'screwed on to a casehardened (finish) receiver.

When Krag 'barreled-actions' were refinished, they likely were left together with action and barrel undergoing the same 'browning' (bluing) process.

Thank you for the explanation. On my two krags I guess the rebluing  seems to have wore off the case hardened reciever. The mottled colors are visible again.  On the inside there is the area missing the bluing. Maybe it's just the way the bluing reacted with the case hardened steel verse's the untreated barrel steel.

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Inside

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Those lines are not smooth the way you would think if they were dipped in a bluing solution. Could they be from case hardening pack not completely filling the box? If so the are not completely cased may take the bluing differently?
In the ancient past case hardening was done by packing and sealing clay jars full of the carbon bearing material with the item being hardened. The jar was expendable and broken open when the process was finished. Any reading material available on how SA did this to the Krags. It has already been said on this forum that surfaces than needed to be extra hard and wear resistant were painted with cyanide during casing, but no mention was made of the other details.

Reviewing earlier posts and Mark's mention of bluing sand fits the irregular lines very well, if it settled or the receiver was not completely filled. Maybe someone can elaborate on the process as I have never seen it described.

Two issues of Scientific American (1899) described the manufacture of the Krag and appear in Mallory's "The Krag Rifle Story".

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For those that have a hard time reading fuzzy text on a computer screen the answer is cast iron boxes.
Thanks BR.

Still interested in bluing sand. Is that just plain sand held at temperatures to get a blue oxide, or is the sand infused with something to get a blue at a lower temperatures?

For anyone wondering why Krags would be difficult or impossible to build today, the article says 120 different machining operations were involved. Each one necessary and carrying the risk of scrapping the receiver.

Note that the quench of case-hardened parts was in oil, not water. The result was a dark mottled gray/black surface, not bright colors. With time and handling this often fades to a light mottled "silvery" appearance. (Bolts were polished bright after the quench, apparently.)

In contrast, parts "browned" (rust-blued) at overhaul have a uniform black (or blue-black) finish without much/any mottling. It is significantly more durable in use than the original oil-quenched finish, frequently remaining quite dark after 100+ years.

Since the "browning" process can be done by any competent tinkerer with a metal tank long enough to boil the barreled action in water, it's sometimes near impossible to tell if a decent rust-blue job was performed post-service. Often the main clue is that many would-be restorers can't resist the temptation to polish/buff surfaces far more than the armory did.

Three photos taken at Springfield Armory - Hill Shops - 'Hardening Room'. I believe the pictures show: hardening of 1903 Springfield receivers-in iron boxes (1), hardening of 1903 bolts in tray (2), and possibly installation of extractor-ring on 1903 bolt (3).

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"bluing sand"? - I think possibly that is a 'typo'.

Maybe Mark's post should read: "bluing and ...."

"Parashooter", thanks for your insight on (SA) Krag original finish and arsenal re-finish.

King Carp, maybe your pictured Krag receiver has its original casehardened finish? That light colored area at the front of the magazine floor looks like case-color to me.

FWIW - Attached photos of 'New Old Stock' model 1898 Krag bolt. The recessed bolt face and groove to clear ejector show "black" from heat-treat. The remainder of bolt is 'in the white' from SA polishing.

Grandpa's Gun Parts has NOS bolts, as well as, 'parkerized' bolts, that must have been a WW-1 period development.

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I am sure Mark's post is a typo. "bluing and"not sand

""bluing sand"? - I think possibly that is a 'typo'.

Maybe Mark's post should read: "bluing and ....""

I guess that explains why I never heard of it before. Too bad it was not a real thing as it would have been a good explanation.
I have made so many typos, that when I go back and look at my old posts I am sometimes not sure what was intended. I usually look over what was typed before hitting the Post Message button but I see what I intended to say instead of what is actually there.

BR, on your 3 photos #1 definitely look like cast iron packing boxes in the lower right.
#2 on the bolts maybe that is a tempering operation? Ovens are completely different. Looks like the bolts are just stacked in similar boxes. Look at the boxes of bolts on the floor. First ones in are upright and later ones leaning over?
#3 Must be winter time. In the summer I would have wanted that work station a long way from that hot stuff going on behind him.

I am just taking a stab at making sense out of vague assorted SA photos.

Wonderful & beautiful arms were constructed in dismal looking Springfield Armory shops!

Take my comments as guesses also.
Labor must have been cheap back then. My father told me about baling hay for $1.00 per day at the end of the depression. Must have been much less at the arsenal during the late 1800s.

Actually, I believe, Springfield Armory jobs were rather desirable and the talented labor force had long careers at the Armory.

Manufacturing has usually paid higher than other jobs. Would have expected the same at SA. Costs of everything was lower. You posted that list of prices for component parts for the Krag. Compared with today's costs they were disgustingly cheap.
Comparing apples to oranges a Krag probably cost 15 days wages, a Remington 700 today cost probably 3 days wages.
My mother used to pay 10 and then 25 cents for my haircuts when I was a kid.

The Connecticut River Valley was quite the industrial powerhouse with many famous manufacturers attracting skilled labor.

FWIW -  The Annual Report of the Chief of Ordnance for 1895 mentioned 'profiling' had a minimum pay of $2.00 per day, some milling operations paid as little as $1.00 per day, highest level was $2.50 per day for some polishing, milling, drilling, and filing operations.

I'm sure there is much more known on pay scales for various armory jobs.

BR,
Those figures sure mess with my calculations. If I am remembering correctly the cost to make one rifle or carbine was $7.50. The $2.50 guy could have bought one for 3 days labor if they were for sale.
Wowsers!

bluing sand was definitely a typo.

Have a great day all!

Mark