Since the bulges are at the bottom of the barrel, the loose shot theory makes some sense. I sure wouldn't call this rivelling. I have heard that the juddering that rabbit mentioned may be caused by excessive oil left in the bores which causes a hydraulic deformation of the tubes when it gets trapped between the shot column and the barrel. An L. C. Smith I owned that had a rivelled barrel didn't get any worse from continued shooting.

Voting for anti-gun Democrats is dumber than giving treats to a dog that shits on a Persian Rug