ORIGINAL: The Rifleman
The only way you can shoot 3 inch magnums in a Model 1100 is if it was designed for 3 inch magnums.
You cannot shoot 3 inch magnums in a 2 3/4 inch reciever because the ejection port and the magazine and the reciever is different between the 2 3/4 and 3 inch magnum guns.
well i can
i dont know how my dad made to where i can but he bought a barellel that they dont make any more (because it allows you to shoot 3")