Check out - TARHUNT. COM its the site for tar hunt slug guns and light field slugs . It has a section on shooting slugs that addresses alot on how to shoot slug guns , it helped me and you might find it helpful .
i shoot a savage 210 slug gun . Have tried a bunch of slugs and settled on lightfield 3 inch , have had really tight groups with them , a few in the 2-2.5 range but avg. 3-3.5 . I know there are folks that get 1/2 inch groups but i haven't figured out how to with slugs approaching 3/4 inch in dia. And yes a few groups of 3 were clover leafs but can't do it on demand !
have noticed that some lots of ammo are tighter than others .
i use the three inch shell because it feeds thru the savage the 23/4 sometimes don't . can't say what the receiving end feels like but the launching end get a bit mo kick with 3 in. shells . if your gun shoots 23/4 good , stick with them you are a lucky man !