3 inch chambering wasn't not around all that long ago.. The 3" and 3 1/2 inch popularity are a product of the Non Toxic shot laws for waterfowl. The theory was steel is less dense than lead so you have to compesate by going to larger shot.. Then you reduce your pellet count so the only way to get more pellet count is to increase the lenght of the shell..

I have about 6 O/U ranging from the 410 to a 12 guage.. My 12 is chambered for 2 3/4, 3 and 3 1/2, but I rarely use 3 1/2... For clay shooting I use the 28 or the 410.. Hunting I use the 12 or 20..

Each gun will pattern a little different with each load..