Having a brass barrel I have no doubts about quickly wearing down the rifling using steel bb's, but I'm sure you'd get high velocities. If you happen to find lead bb/round balls (gamo?) you might get a feel to the accuracy that can be had before trying to convert to shooting steel. I believe there once was a smooth bore Benjamin in 177, but don't recall the model. If wearing out the rifling is of little concern to you, I think the 397 is an excellent platform and shoot whatever you want from it. Especially if it's a newer synthetic 397S, I don't think you'd ruffle too many feathers doing so.
The only thing contacting the barrel is a linen cloth patch around the BB.