Having a dedicated slug gun or at least a slug barrel on your shotgun will significantly improve your accuracy. These barrels are fully rifled to provide the best possible accuracy. I understand that money can be an issue along with possible hunting regulations against rifled barrels...in that case the Brenneke rifled slugs (suggested by
@Wyatt Smith) are the best option IMO.
My friend bought a Savage 220 and put a Leupold 1.5-5x20 on it with Warne rings. His total investment was right around $1200 with MOA accuracy out to 100 yards with Federal Trophy Copper 275 grain Sabot Slugs. Perfect for his Whitetail Deer hunting needs in the forests of Upstate NY where rifle hunting is not allowed.
FYI - Smoothbore barrels use rifled slugs. Rifled barrels use sabot slugs. Rifled slugs should not be used in a rifled barrel because there is not enough contact between the lead and rifling to create spin. What happens is the lead from the bullet fills the rifling on the bore after just a few shots. This essentially makes it a smoothbore or at least a PITA cleaning project. Ask me how I know...