I would recommend the Remington 870 Express Tactical, or the Model 870***8482; Express® Tactical with BLACKHAWK! Spec Ops II. Remington makes a great shotgun, and they're very durable. 12ga is the only way to go.
As for accessories, an adjustable Blackhawk or Mesa Tactical stock is a must these days. They're very good for reducing recoil and adjusting LOP. A side-saddle shell carrier is a necessity, and I highly recommend a Mesa Tactical saddle setup.
For ammo, I'm a huge supporter of 00Buck. Given everything that I've seen for information, buckshot is the best option across the board for the shotgun. I prefer tactical loads like the Federal Tactical buckshot with Flite-control, but the Hornady TAP shotgun loads are high quality as well. You can put all pellets inside of a pie plate at 25yds.
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