I had a Stevens M311 20 ga that I bought new in 1963 or 64. I sold it in the early 80's. It never ever had any steel shot run through it, only lead loads and virtually all one ounce field loads. Way less than a box of three inch 1 1/4 ounce loads. A grand total of maybe 300 shells, probably much less. Both barrels had a very slight ring bulge about one inch back from the muzzles. They were quite slight but nevertheless easily visible. And oily barrels were definitely not the cause or a contributing factor in this case.
