Cimarron Billy Dixon 1874 Sharps 45-70 Gov, 32" Barrel, 1rd

First time out to the range, I used the set trigger and the firearm went off. I thought that maybe I had bumped the front trigger by accident. Second time I thought maybe I did not get the hammer all the way back before I let it go. Third time I knew I had a problem and now the hammer very consistently drops without the trigger ever being touched. This is the primary concern, my secondary concern is the sights were so far off at 100 yards that I could not hit a 2ft target if I aimed dead center. The gun was shooting roughly 20in high at 100.