Turns out that Franklin B. Warner was President of Kirtland Bros. & Co. at 96 Chambers St., New York City at least until 1921
https://books.google.com/books?id=HIkoAAAAYAAJ&pg=PA155&lpg
https://books.google.com/books?id=HeMcAQAAMAAJ&pg=RA5-PA27&lpg
https://books.google.com/books?id=72q1bWJDhFYC&pg=PA326&lpg

That might explain the tradename guns. Manhattan Arms Co. was a trade name used on hammer and hammerless side by sides imported by Schoverling, Daly & Gales, Kirtland Bros. Co., and Von Lengerke & Detmold, all of New York City. The guns were made in Belgium by Neumann Freres and Fabrique d'Armes Fs. Dumoulin & Cie, and in Germany by J.P. Sauer. SD&G also had a Manhattan Arms Fulton.

1918 "Davis Guns & Warner Pistols" by Kirtland
https://books.google.com/books?id=mCgDAAAAMBAJ&pg=RA2-PA122&lpg

Cornell Pubs has a 1924 catalog; nothing earlier
https://www.cornellpubs.com/old-guns/item_desc.php?item_id=413

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