Without a photograph, it's all just speculation and a barrel is just a barrel, unless it's in a stock.
Governments have been stamping their property, firearms and parts, for, literally, hundreds of years.. Civilian gunsmith's shop have almost always had lots of different parts, laying about, of unknown origins, including surplus military.
Anything is possible. It could have been a Civil War barrel and then again, it could be from just about anything prior to the early 1900's.
I love seeing stuff that people find in and around abandoned buildings and properties and it would be neat if we could get a photo.