[Bug Doc]

...While I generally like Remingtons, my brother has the 3 1/2" 11-87 and he tells me that you have to take the gun apart and do something with the gas system to go from a 2 3/4" to a 3 1/2" load. ...

What he is referring to is a part called a piston seal activator. It is an additional ring you can install to help the Super Mag cycle light target loads. It works by seating the rubber O-ring tighter and partially blocking off the pressure compensation ports. Without the activator Super Mags will cycle typical 2-3/4" field loads (1-1/4oz 1330 fps) just fine. Most will also cycle heavy target loads (1-1/8oz 1300 fps) without the activator installed.

To answer the original question, I've also hunted waterfowl for decades using autoloaders (mostly Remingtons but also Berettas and Brownings). Keep 'em clean, use appropriate ammo, and you'll love 'em.