I think the term swamped simply means "sunken". Most modern swamped barrels are as described above. But I consider a barrel that does not flare at the muzzle, yet has sunken flats, to be swamped. That is a barrel that tapers at a slower and slower rate toward the muzzle, so that the flats are sunken, as opposed to straight tapered. This yields a barrel that is heavy at the breech for strength and balance, and is still lighter than a straight tapered barrel.