This box is very near the vintage of the gun --
NITRO CLUB 24-gauge load side 2-piece.jpg
NITRO CLUB 24-gauge notice side 2-piece.jpg
NITRO CLUB 24-gauge top 2-piece.jpg
I have never seen any U.S. Cartridge Co. 24-gauge shells, and I have four Cornell reprints of U,S, Cartridge Co. catalogs 1912, 1914, 1916 & 1917 and a 1920 Revised Price List and none offer a 24-gauge shell or NPE.