The difference between the 2 3/4 inch chambered guns and the 3 inch chambered is the ejector assembly. This part in the 870 is pinned to the inside of the receiver. At some point Remington quit making the shorter 2 3/4 ejector and the part numbers for the 2 3/4 and 3 inch were the same. It is possible to change out the ejector if it is the 2 3/4 inch version and install a 3 inch chambered barrel. Installation of the ejector may require re-bluing the receiver. The expense is usually great enough that simply buying a 3 inch 870 is cheaper..and you needed an excuse anyway, right?