Found this a while ago, curious to the make. All I can read on the barrel is "ADD.... YORK...US(A?)
I know it's not much to go on, but you guys are great at finding this stuff out.
Curbdiggercarl
Some of the Colt pistols of the 1840's-60's had barrel markings that match up with the lettering you describe [ ADD.... YORK...US(A?) ], as shown below: