remington 870 express magnum

[Kidder]

Im a little confused and worried about shooting 3" shells in it.
this is what the barrel says: use 2 3/4 or 3" shells in magnum receivers. Use only 2 3/4 in all others.

could someone clarify on what that means and if I can shoot 3" shells out this.

 

[Pa Grizz]

Call Remington at 800-243-9700.Most new shotguns are made to shoot 3 in,but not knowing your gun I would call them with the serial number