I've been searching for a couple of weeks now for an original sight base without luck (it almost happened, but that's another story!).  I've decided to take the advice of a couple of you here and go with the repro from S&S, which I ordered.  Since it's in the white, I'm wondering what others have done as far as bluing it.  I ran across a reference online that these were originally oil quenched and was thinking about trying that.  I've never blued a gun part in my life but think that any modern bluing is likely going to look too blue.  Any experience others have had with this that worked well and ended up blending reasonably with the existent aged bluing of the Krag barrel?

Thanks, that sounds like a pretty good recipe.  So the combo of the browning and bluing gets you close to that plum color, which I guess makes sense.  I should confess I have a form of color-blindness, so I'm always cautious about discussing color.  When I look at the barrel I see the blue (which is in the good part of my color spectrum) but it also seems to have a brownish hue to me too.

I should back up a step as I have had some experience browning barrels.  I hot browned my Pedersoli Brown Bess barrel, or at least helped while a couple of buddies who knew what they were doing showed me the ropes.  I also cold browned a DGW American Jaeger kit rifle, which turned out really well but you're right, it's more of a golden or maybe copperish brown.  I still have some of that DGW browning soln. left over.

It would probably be instructive to find some scraps of a similar metal these site bases are made of and play with the recipe a bit to see how it affects the final outcome.  

I really appreciate the suggestions.  In the meantime I've been spending way too much time searching and reading about various forms of bluing on the 'net, all over a 1X1/2X1/4" part!  It seems "all roads lead to Rome" though with different caveats, durability, rust resistance and end result colors.  There's a lot of excellent step by step instructions I've run across from machinists, gunsmiths, blacksmiths, period blade makers, and other hobbyists.  Rather fascinating actually.

Once this part arrives I think I'm going to try oil quench bluing it and then probably follow that with the browning solution, with final dip in the boiling water and carting as you described.  As long as I don't do something too stupid, worst case scenario is taking it back to the white and trying again.

DocCasualty:  Original Krag sight blades are generally .050" thick.  The slot in the sight base gives a snug fit to the blade (so there is no wobble when fully installed).  However, you should be able to easily start the blade into the slot and easily able to tap the blade into finished position with a light plastic mallet.  I would recommend you lightly sand  the inside of the slot of your base so the blade can be easily started into position.