a few common slug gun mistakes I see at the range.

-trying to sight in or get groups w/out a rear rest
-resting the the forend(pump) on the bag(not a stable platform) rest on the magazine tube/receiver instead
- holding the gun too loosely ,pull the buttstock back tight to your shoulder.
-using cheap scopes and cheaper rings and mounts, they just dont hold up against 12ga recoil.

I would agree on lightfields too they work well in almost all guns, brenekee KO sabots aswell. rifled slugs in a rifled barrel arent a great idea iMO due to leading in the barrel. theyre designed for smoothys