Worst peice of abuse I ever saw was on a surplus "Turkish" mauser that I bought when I was 17; I still haven't figured out if it was a '93 or a '95, but the thing shot patterns that would do my 870 proud! The bore was so rusty and pitted that it would barely pass as a water pipe (and that is all it was good for). Whoever did the rechambering job (from 7.65 Argentine (I'm guessing) to 8x57 didn't do to great a job....the cases were always cracked when I extracted them. The front sight would turn 15 degrees to the left and 10 degrees to the right, and when I pulled the barreled action from the stock, about half the Sahara desert fell out of that gun stock!
I ended up using that rifle to "practice" my gunsmithing skills!