passenger list grandfather

Im still trying to find what ship my grandfather came over on, in the 1900 census halfan gunnerud his father hans and mother hanna are listed, i know he had to come over in 1910 the port Boston, he settled there and is listed in the 1920 census. I have contacted NARA and they reseached the ship list for me and with no luck they could not find him on a ships list. Ive done a ton of research and can not find any information on him being a passenger. Whats my next step? Where do i go from here. He was born 1892. Thanks Kim Foster