Winchester barrel markings were CT. until 1886 and then changed to USA. I was told they changed it due to patent infringement. The barrel was made before 1886, but it could have laid around the factory until 1889. T/R

  The 1886 change from CT. to USA applies to octagon barrels, I’m not sure about round barrels and carbines. My experience with 1873 and 1876 has been octagon barrels. I look at the barrel address, the sights, upper tang marking, and serial number to determine if they match. A USA barrel address on a pre-1886 gun is a red flag but a CT address on a post 1886 gun is not. T/R