BudsGunShop.com - chamber size ?

yes you can use 2 3/4 shells in a 3 inch chamber however in some older semi auto shotguns (Remington 1100) the 2 3/4 shell will not work the action to chamber the next shell more modern designs (Remington 11-87) have a gas compensating system that allows them to fully function with both 3 and 2 3/4 shells

Hi,
In most modern shotgun, 3 inches chambered shotguns allow usage of 2 3/4 rounds. Unless specified by the manufacturer, 2¾" rounds and 3" are interchangeable. Exception would be some semi-auto and older shotgun. Cheers.

This is true you can use 2¾" rounds in most all 3" chambered shotguns ( unless the manufacturerstates otherwise), but not vice versa. If you have a Shotgun with a 2¾ you cannot fire 3" shells.