This note may be too late to add anything, but I'll post it anyhow: the only ring bulge I've seen so far was in a Model 12. Maybe the Heavy Duck model has a thicker barrel (I don't know), and maybe a choke other than full could prevent this type of damage. But the standard 12 gauge full-choked Model 12 I inspected did have a rather hideous ring bulge behind the choke.

Quid me anxias sum