you can put a 3'' in a Remington 812 2 3/4" but eventually it'll blow the barrel, wouldn't recommend it.
If it's a 16 gauge shotgun, the shell length is 2 3/4 inches.
Remington makes a model which does.
Remington makes a model which does.
3"
the shotgun takes a 2 3/4 shell
Remington makes one.
Remington 870 Express Super Magnum.
If the gun is marked 2-3/4 on the barrel, that is the maximum length shell that the gun will shoot.
The Iver Johnson shotgun, model 410 Champion, typically has a chamber length of 2.5 inches. For this model, the required shell length is also 2.5 inches. It is important to use the appropriate shell length to ensure safe and effective operation of the firearm. Always consult the manufacturer's specifications or a knowledgeable gunsmith for any specific concerns.
The shell length that the chamber can handle should be stamped on the barrell.
The Bay State .410 shotgun fires a .410 gauge shell, the smallest of shotgun shells. The shell itself is around 3 inches in length.
You can download an owner's manual for free at Remington's web site.