A gentleman selling older rifles at a recent gun show told me that the metal finish on early Springfield's including Krags was basically a coating from oil in the quenching process that wore away fairly quickly.  In other works, there was no chemical reaction as with various bluing processes.  He said the mottled black appearance so common in older firearms was simply remaining areas of this coating.  I have a rebarrelled Model 1896 with a really nice even finish all over.  Per this gentleman, virtually any rifle looking like mine has been blued in some timeframe after it was originally made.  Is this correct?

Thanks, Butlersrangers!.  I was aware that the receivers and some other parts were case hardened but quenched in oil rather than water.  The color variations in the common case hardened steel is due to intentional uneven quenching.  The different colors represent steels of different crystalline structures.  I was always under the impression that the color from oil quenched case hardened steel was a uniform outer layer of steel of a particular crystalline structure that had a gray-black color.  But I was told recently that the dark, uniform color was due to the burnt or coked oil.  The coating theory seems feasible as a uniform layer of steel from the quenching would be thicker and more durable.

Let Larry Potterfield, from Midway, show you how its done...

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I often thought about sending a beat-up old Krag to Turnbull Restoration and letting them have their way with it.  They do beautiful work and the color-case-hardening is IMHO outstanding!

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BEWARE when monkeying with case hardened parts!  As the name implies the hardness is only so deep... so when you start sanding and filing dents/imperfections you maybe removing the case hardening.

Here is about as good as it will survive on a U.S. Krag:

OOOOOOO, nice pretty colors on the butt plate!    I'm going to have to try that!

Rust bluing is by far my favorite.  I think it imparts a rich, dark, deep blue and, I agree, is the more durable finish.

Cold bluing gets laughed at but you still can get good results.  I use it a lot on small parts and touch-ups.

Plum Brown works great for getting something to look old with a nice even, kinda mottled brown patina. Like an old musket barrel or socket bayonet.  Actually, I get confused sometimes because the word browning is also used to describe the brown finish applied to really old firearms. 

Just to reiterate what 'AFJuvat' and I have said, the "browning" process, in Springfield Armory references, was rust bluing. (Also, the color and appearance are quite different than hot caustic bluing and other modern finishes).

Of course, what we now refer to as "browning" has been utilized on firearms, since they were invented.

This thread made me think of something else:

I see a lot of old guns with buggered screws, some of which can be hard to replace. I've not seen it discussed on any forums, but an old machinist showed me a trick which can work wonders. You have to choose your projects, of course. Some should be left alone, and some are too far gone, but there is a broad middle ground which will benifit from the work.

Grasp the screw in a vise, between blocks of wood. Get a small ball-peen hammer with a smooth face and start tapping at an angle on the screw head, bumping the metal back into place. You also need (to renew the slot, which will frequently close up from the tapping) needle files, a sharp fine hacksaw blade, and perhaps a Dremel. Polish with emery cloth before refinishing. No two cases are identical, and the fix may not be "perfect" but it can often produce a huge improvement, on a middle-grade gun.

Practice your technique on a few worthless screws before you tackle something important. The key is the tapping, to return the slot as close as possible to its' former shape - just polishing off the burrs (as is sometimes encountered) doesn't do the job.

Great pictures. Thanks.