Here's the law. It is Federal. States must comply.
http://cfr.vlex.com/vid/20-21-what-hunting-methods-are-illegal-19894510I confirmed that many 3 1/2" shotguns come with plugs that limit the magazine to two 3 1/2" shells but allow three 2 3/4" shells.
Migratory birds on which open seasons are prescribed in this part may be taken by any method except those prohibited in this section. No persons shall take migratory game birds: (a) With a trap, snare, net, rifle, pistol, swivel gun, shotgun larger than 10 gauge, punt gun, battery gun, machinegun, fish hook, poison, drug, explosive, or stupefying substance; (b) With a shotgun of any description capable of holding more than three shells, unless it is plugged with a one-piece filler, incapable of removal without disassembling the gun, so its total capacity does not exceed three shells. This restriction does not apply during a light-goose-only season (lesser snow and Ross' geese) when all other waterfowl and crane hunting seasons, excluding falconry, are closed while hunting light geese in Central and Mississippi Flyway portions of Alabama, Arkansas, Colorado, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, New Mexico, North Dakota, Ohio, Oklahoma, South Dakota, Tennessee, Texas, Wisconsin, and Wyoming.