A few comments on the above comments. First, the fella with the Jambmaster 870 was without a doubt shooting a cheap Express model of later vintage. For years Remington kept making those with rough machined chambers that would grab shells and jamb or fail to eject. It's an easy fix at the gunsmith. Some folks fixed it themselves with drill and polishing compound. What's less easy to fix is the crappy metal and finish that rusts if you sneeze on the gun. As I said, 870 is a good workhorse ... just stay away from Express models unless you know it's an older (very older) model.
Next, don't shy away from a nice older 12 gauge Wingmaster with fixed full choke. Lots are available relatively cheap. Factory fixed modified were more uncommon and now more in demand so they usually bring a higher price. For starters there are TONS of aftermarket choke tube barrels available for 870 at very reasonable prices. As I mentioned above, reaming out a fixed full barrel to modified is a cheap fix (probably only slightly cheaper than just replacing the barrel). And finally, you can shoot steel through a fixed full 870 barrel. I did it for most of thirty years. It's one of the few factory barrels built tough enough to take it. Modified gives a better pattern but I killed hundreds of honkers with mine. Just don't shoot bigger than BB steel or more gas than 1550 fps. You can find this verified numerous places on the web. But if I still shot that gun I would probably get another choked barrel for it because I now hunt a helluva lot of uplands and shoot a lot of skeet.
A 3.5" gun has a receiver that is half an inch longer (even designated 2.75" older guns usually utilized 3" receivers). A longer gun is no fun to carry and a longer action doesn't cycle as efficiently. It's all unnecessary. In the unlikely event that you decide to undertake the enormous expense of getting into waterfowl hunting (decoys, calls, blind, DOG, etc.), MAYBE then consider stepping up to a huge, brutalizing, expensive to shoot, totally unnecessary, designated goose gun. But a fixed breech 3.5" cannon? No. If you go that route, get an auto or you will be unhappy ... out of money and likely physically hurt. Shoot a 3.5" once and you'll see what I mean. Add to that the fact that almost all 3.5" guns are relatively new and, for whatever reason I will NEVER understand, purposely designed to be lighter weight. A pump action is generally always lighter than an auto. Lighter = more felt recoil. In the case of 3.5," a fixed breech, lighter weight pump gun will have MUCH MUCH more felt recoil than an auto. Years ago I put my 870 3" magnum away because I am one of the unfortunate few with fragile retinas prone to spontanious detachments (three in the left eye and numerous tears in both eyes). I bought an old Browning A-5 long recoil semiauto 3" magnum with 31" barrel, specifically because it's probably the heaviest twelve gauge shotgun ever made (for weight it was a close race with the old magnum Remington 1100s but those guns could ONLY cycle 3" shells). I later switched my A-5 to plastic for durability but added weight to compensate. I'm guessing it's still nearly ten pounds unloaded. Besides being safer for my eyes, I shoot a heavier gun better. Less inclined to flinch and it swings better. Light guns are too whippy. Anyway, every once in a while on trap league days when weather is really crumby (like today!) I'll dust off the battered old 870 to shoot a couple rounds. After the first station of shooting mere trap loads I always ask myself how the hell I put up with that brutal jarring for decades. I simply cannot imagine the punishment 3.5" shells would dole out in that gun!