ive shot an obrez before... guy had it rigged with an ar pistol grip it was insanity. hands down worse than 500 smith snubby (the next closest thing to biggest recoil I have shot). I would shoot the 500 again, but I still have nightmares about the obrez.
http://www.youtube.com/watch?v=0Zn2MIgGbNE
http://www.youtube.com/watch?v=0Zn2MIgGbNE