Ring bulges in the choke area, some of which were reported with steel loads (especially early ones with less protective wads) being shot through tight chokes, are pretty much a cosmetic issue. Pressure is so low out there that nothing is likely to happen. They're unsightly, but not very likely that they're dangerous. After all, we shoot guns with holes at the muzzle (porting) without any concerns.
Someone earlier suggested that a bulge within the first 18" or so is a definite cause for concern. I'd agree. I'd also agree with Miller that fixing dents is often fairly easy. I used a hydraulic dent lifter on quite a few, always being careful not to bulge the barrel.
