In December 1896.
Frank Munsey's The Argosy publishes its first all adult fiction issue, pioneering the pulp magazine genre in the United States. The name was changed to Argosy All-Story Weekly in 1920 after the magazine merged with All-Story Weekly, another Munsey pulp, and from 1929 it became just Argosy.
https://en.wikipedia.org/wiki/Argosy_(magazine)
The Argosy (from 1891 till 1922) is available at HathiTrust:
https://catalog.hathitrust.org/Record/006062033