Kimberman said:
The heavy shot I have shot was reloaded by a friend of mine (2 3/4"), and if I took up duck hunting I have the equipment to reload my own. Plus being from E TN, you MAY shoot a box of shells a season, so the cost doesnt scare me all that much. Then you have to figure trade offs, the 3.5 inch chambered shotgun is a little longer and a little heavier, both attributes you dont want if you are quail/rabbit/grouse/chukkar/pheasant/woodcock hunting. I have been an avid shotgunner for the last 23 years, and I have made it this far without needing a 3.5 inch magnum.
I could easily see going thru close to 2 boxes of 10 at $30 a pop on a good day. I'd probably want to carry 3 boxes to be on the safe side. Even when reloading, its still expensive. It goes for around $150 for a 7 lb bag so you are still looking at close to $2 a shell. Also, if you compare the remington express 12ga with the 28 inch barrel to the 870 supermag, there is no difference in weight and length between the 2.
That all being said, I have been duck/goose hunting for over 20 years and have never owned or felt the need for a 3.5 inch gun. My point was that there is some advantage to the 3.5 shells.