You get a yes and no answer, normally not needed on a cantilever set-up, unless you have play between the receiver and barrel.An old trick, drill and tap the receiver and the barrel lug and bolt them together, if any slop exsists which could change point of impact once you screw them together it will remain a pair as long as each time you put the slug barrel back on, you put the screw in place, point of impact will stay constant. When useing the smooth bore put a blind screw in to protect the threads and cover up the hole. If it is a newer shotgun with a cantilever mounted scope it will take a while befor it has enough slop to worry about it, most problems Ive encountered are on older alluminum receiver shotguns, the 870 should last a long time befor this fix will be needed. Something to add!, most times receiver to barrel slop occurs is when the mag cap is not tightend enough letting the barrel move in the receiver. Most gunsmiths should be able to preform this fix.