I would say, no, that is not a bull barrel on that 597. It looks like a .620-size, which is about average. A bonafied bull barrel is one that is .920 or larger, and some consider slightly smaller barrels (like the 917v's .820-size) to be bulls. That's largely the reason why I bought my 917v. They are stiffer than regular barrels, and don't whip around like a noodle as much as thinner-barreled rifles do. Also, they take longer to heat up from fired shots, so they TEND (not a rule) to be more accurate than thinner barrels. Flutes also help to dissipate heat better.