I often wondered about the durability of cheap singles too. I have a Stevens double from the 1930s that I bought for dog training from an old dairy farmer. Really rough and the last 3 inches of the barrel bulged like a cartoon. Sawed off the bulge and it has been my utility/dog training gun ever since. Obviously abused, it still is tight as can be. The barrels proudly say "barrel and lug forged in one piece" so I guess it has a "chopper lump" barrel!