The Mossberg Rifled barrels are fair barrels.
With good glass and the right slugs you should have a solid 150+ yard big game gun.
I like the Remington Core-Locked Ultra Sabots...Controlled expansion and 1900 fps with good accuracy. In most guns you could expect to shoot 4-5 inch groups.... minute of deer.
Of course some are better than others... the quality of the trigger, how and where the scope is mounted, the marriage of the barrel to the reciever, barrel length and harmonics as well as the rate of twist all come into play with accuracy in slugguns.
Here is the most important advice for sabot slug shooters!
If you don't clean the plastic fouling out every 6 shots you might as well throw stones because your accuracy will be that bad. And any regular solvent will not touch the plastic fouling left by sabot slugs... you must get some sabot solvent for this job!
Shooters Choice Choke Tube and Barrel cleaner for Plastic works great!