I've done a significant amount of shooting with rifled barrels and sabots slugs. I have a Browning Abolt 12 ga which is a dedicated slug gun, a custom Remington 1100 20ga, and a Benelli Blackhawk. They all shoot different but there are several guidelines to follow to obtain maximum accuracy. First, keep in mind that we are asking a lot out of a little piece of plastic(sabot) traveling down a rifled large bore slug barrel at anywhere from 1450 to 2100 fps. Not only does it have to grab the lands and groves to create the spin necessary for accuracy upon leaving the barrel, it also has to hold the projectile and then cleanly(most cases) disengage 10-35 feet from the end of your barrel. Some sabots are permanently attached to the bullet but you referenced Hornady SST's which are not. Secondly you must keep that barrel clean which in my experience means every 4 shots. At the range a bore snake and solvent will do until returning home for bronze/brass brush with JP bore cleaner or super blue wonder, solvent and patches, dry patches then finally a very light coat of Kroil. At which point the firearm is stored barrel down in my safe(oil/solvent runs out instead of into action or stock). You have to keep the barrel from heating up while firing at the range. I wait 5 to 15 minutes between shots depending on the temperature at the time. This step is just as important as cleaning every couple shots. You need an absolute solid rest. I use sand bags made from empty lead shot bags. I use good quality scopes boresighted by by gunsmith. You cannot adequately sight in at 100 yards without magnification. Lastly, you have to find a brand that your gun will shoot. My Browning shoots Federal Barnes Expanders very accurately, 1 1/2" at 100 on my best days. My custom Remington 20ga is currently shooting Federal Barnes also but is far more finicky due to the lighter weight barrel and that the barrel is removable(even though it's pinned) as opposed to the Browning Abolt(bolt action shotgun designed only to shoot slugs) but still shoots about 2 1/2" at 100. The Remington also shoots Hornady SST's well but I like the terminal performance of the Barnes bullet. I will be 'tweeking' this gun this summer into fall possibly going to the Wichester line. My Benelli which is used by my son is the most finicky, it will not shoot Winchester or Remington sabots(Gold line, Copper solid and Buckhammers). It does shoot Lightfield's the best but I don't like their performance on deer. They do not exit even at 25 yards and in my experience(7-8 kills with them) leave less than desirable blood trails. We settled on the Hornady SST's for the Benelli which give acceptable accuracy and good terminal performance.
As far as shooting foster type slugs through your rifled barrel, you will not harm it according to my gunsmith. It will just clog up your barrels' rifling turning it into a smoothbore. Yes good hard scrubbing with bronze/brass brushes and solvent will clean most of it but micro-specs will remain and can only be seen by a bore sight. Also remember that foster type slugs are made very slightly undersize in case they're shot through a full choke. Rifled barrels on the other hand are full bore. This leads to the question of how much spin(where accuracy comes from) is placed on a rifled slug in a rifled barrel? I can't answer that. My gunsmith will tell you that the most accurate action/barrel/slug combo custom made by him that he sells is a Remington 870 with a pinned screw in choke barrel, rifled choke tube and a brand of foster type slugs which I do not remember at this time. He qualifies this set up by stating it's a 100 yard gun ONLY. After 100 yards the accuracy for some unexplainable(by him, I have no clue) reason goes all to hell. I hope this helps some and good luck.