A seal assembly between a wellhead housing having a bore and a casing hanger, has an inner seal leg for sealing against a hanger and an outer seal leg for sealing against the housing. A bellows style portion is formed on a nose ring carried by the seal assembly to increase lockdown capacity. The bellows style portion has an inner surface that faces an outer profile of the hanger, and an outer surface that faces the bore of the housing. Inner and outer lock rings are disposed on the bellows style portion. When the bellows style portion is axially collapsed, it radially expands into the bore of the housing and the outer profile of the hanger, and urges the inner and outer lock rings into engagement with the outer profile of the hanger and the bore of the housing.