In that the .410-bore 3-inch shell was introduced in mid-1933 along with the Winchester Model 42 pump gun, 1934 is probably a good date. That is when Ithaca Gun Co. began chambering their .410-bores for the 3-inch shell. Lots of earlier .410-bore guns were likely sent back to factories for 3-inch chambers, Ithaca Gun Co. offered that service, or were hogged out by local gunsmiths.