Best I can find is a reference to JH Johnson and Great Western Gunworks is that he was born 1811 and died 1889.(This was listed in an ad trying to sell a rifle with these markings. I don't know where the seller came up with the info.) I find it a little curious that there is both a makers name and a business name on the barrel. Sounds more like a modern repro, but who knows. Try using Google for Great Western Gunworks and follow the threads, you will find the ad I mentioned.
Dean