To seal an inboard member to an outboard member, a metallic annular seal is inserted into the outboard member to align with an inwardly-open channel in the outboard member. The seal is outwardly expanded at least partially into the channel by a combination of elastic and plastic deformation. The seal is released to allow inward elastic partial recovery. The inboard member is inserted into the seal with interference so as to further outwardly expand the seal and provide sealing engagement between the inboard and outboard members.