I can't say weather or not the gun originally came from Mississippi or not, I don't know the manufacture. On another forum, a poster identified the maker of the gun, stating that he is from TN. He also stated that the gun maker machined his own barrels. As to the type of steel used, I simply don't know.
When I originally posted this, I didn't intend for it to turn into a "pissing contest", was just trying to get some ideas as to what could have happened. The shooter is an old and dear friend of mine and I sold him the gun. I was at the time, and still extremely shook up over this. I am also extremely glad that my dear friend wasn't hurt in this incident. While it's true that over a year ago I double charged the gun, I had shot it probably over 100 times since before selling it, and I'm not sure how many times the shooter shot it afterwards. Knowing him, a lot. He is an avid and accomplished smooth bore shooter, you could almost say it's his passion. I am also sorry I didn't provide enough details. I posted very soon after seeing the gun. I was extremely shook up and a little bit sick to my stomach after seeing the gun and didn't ask any of the basic questions as to load and such.