We need to see some pictures and have the serial number to know which version Ithaca hammer double it is? The original Ithaca was the Baker Model up to serial number 6549, in 1887. The Baker Model was replaced by the New Ithaca Gun in 1887 beginning with serial number 6550. The NIG was Ithaca's hammer gun, produced and serial numbered concurrantly with the Crass, Lewis, Minier and early Flues Model hammerless doubles up to about 1914. A 1910 vintage NIG --
The NIG was replaced by the Two-Bolt Model hammer gun for 1915, which was pretty much a hammer version of the Flues Model hammerless gun. It disappeared from the Ithaca Gun Co. offerings during WW-I.
Ithaca Gun Co. like all of our manufacturers would chamber for longer shells upon request of the purchaser. In the years Ithaca Gun Co. hammer doubles were being produced, our North American ammunition manufacturers offered paper 12-gauge shells in 2 5/8, 2 3/4, 2 7/8, 3 and 3 1/4 inch lengths. As I've stated many times befor, these long shells didn't come with heavier charges or payloads than could be had in the 2 3/4 inch shell, but more and better wadding which many serious shooters considered an advantage.