The heaviest 16-gauge loads offered by Remington Arms - Union Metallic Cartridge Co. in their 1913-14 catalogue were 2 1/2 drams of bulk or the equivalent in dense smokeless powder pushing 1 ounce of shot in their Nitro Club and 2 3/4 drams of bulk or the equivalent in dense smokeless powder pushing 1 ounce of shot in their top quality Arrow shell.
UMC offered to put their 16-gauge load up in 2 3/4, 2 7/8 and 3-inch cases, but the only advantage they offered was more/better wadding over the "standard" 2 9/16 inch shell.
In their 1915 catalogue Western Cartridge Co. listed the heaviest 16-gauge loads as 2 3/4 drams of bulk or the equivalent in dense smokeless powder pushing 1 ounce of shot from their top of the line Record shell.
In the 20-gauge shells one got a 1/4 dram bulk, or the equivalent in dense, more smokeless powder in the long shells, but not so in the 16-gauge?!? Today, finding old long 20-gauge shells in collector ammunition auctions is rather common, but long 16-gauge shells are like the teeth of hens. There is a single Winchester Leader 3-inch 16-gauge shell in the current SoldUSA online auction. I've never seen a box for the long 16-gauge shells come up for auction.