Re: Remington Army 1861 Transitional Revolver
I have never been sure exactly what a "transition" model is; that gun obviously has an older model barrel, simply a matter of the factory using up stock on hand. Otherwise, it looks to me like a standard New Model Army with the loading lever blocking the center pin, the safety notches in the cylinder, etc.
The serial number would be low for the NMA by some books (which give 15000 as a starting range), but if the Beals and 1861 Army are added together they come to only about 8,000 and the New Model continued from there.
(A lot of confusion is caused by Remington dropping the 1861 patent date on the newer gun, so folks call the NMA the "Model 1858", making it sound like it came before the Model 1861, when the reverse is true.)
The letters are those of Remington inspectors, and can be anything as employees came and went.
Maybe others would have better info, but in the condition that gun is in (in spite of replaced nipples, it really looks like it went through a war), I would give it a value of under $1000.