I just got a spare barrel in from a trade; its barrel serial is 30477XX. My first Steyr, and the one I shoot the most/all the time is an M9 and the barrel serial starts with a 0 as the first digit. I eyed the replacement when it came in and something looked different. Compared it to my old barrel that started with a 0. Steyr change their barrel design; more accurately, they changed their locking lug profiles, very slightly. Also, since I never clean my guns, after taking out my old 0 barrel, I realized the feedramped had a decent chip out of the botton of it. The gun has been through tens of thousands of rounds. Just a note.