You can fire slugs from a regular smooth bore barrel though they likely will not be as accurate as slugs fired from a fully rifled barrel and they have considerably less range.

If you want to hunt deer and birds with one shotgun then I suggest saving just a little more money and getting you a combo that comes with a slug barrel and a smooth bore vent rib barrel.

Mossberg makes a model 535 field/deer combo that won't break the bank at about $350. It is a wood stocked, 3.5" chambered gun that comes with a 28" vent rib barrel as well as a 24" rifled slug barrel with rifle sights. The Mossberg shotguns are every bit as rugged and reliable as the 870.

Model number is 45310.