Mossberg makes fully rifles barrels for the 870. I have one on my Express that I use for deer hunting. I like that it is a few inches longer than the other brands.
However, I've not found it isn't any more accurate than my regular barrel with a rifled choke. I clipped on a set of sights onto the barrel and called it a day. My longest successful harvest was at 100 yards. A small deer, spun him 180°, humane and instant. I use the cheap slugs, IMHO for anything past 100 yards, the sabot slugs are required.
Nitro