Remington 870 Trap Shotgun from CarolinaKat from Remington 870 Forum:
The two most common Remington 870 barrels are either the rifled barrel or the smoothbore. Rifled barrels are good for shooting sabot slugs like Premier Accutip Slug, Copper Solid Slug etc. These are the kind of barrels you would use if you are aiming to kill someone or something on a longer distance. Perhaps you want to looking to kill a big predator in the woods. These barrels help you have more stability and accuracy with your shots in order to do this kind of damage. If you are looking for a long range shotgun then rifled barrels would be your best option as well. As for smoothbore barrels, these are more suitable for rifled slugs, birdshot and buckshot. In other words, if you are looking to hunt small ducks or birds hen you would be better off using smoothbore.
RainMan_JH has posted some very interesting pictures of this Remington 870 for trap shooting on the Remington 870 Forum: