Rifled slugs are designed for smoothbore barrels, sabot for the rifled barrels. Twist rate of the rifling on the slug may not match the barrel rifling, reports I have read indicate poor accuracy. Also the muzzle velocity of the sabot also affects the accuracy depending on the twist rate. Remington rifled barrels reportedly shoot lower velocity ( under 1600) sabots best. Remington accutip sabots and older copper sabots were designed for those barrels so shoot the best. Lightfields also performed well from the reports I have read But are no longer made. Supposedly the brenneke sabots dont shoot well in the remington barrels. Drew for a nilgai hunt in Texas that requires muzzleloader or slugs and have a nib 1187 20 ga special deer gun I plan to use and found that I couldnt find accutips so started to research the issue. Hornady ssts are plentiful but supposedly arent as accurate as the lite version. Winchester sells a copper sabot bought a couple boxes of those and the hornady to try thru my gun. Look on ammoseek. Good luck.
I believe this shortage will only worsen as demand for slugs drop as more states ok straight wall rifle cartridges for deer hunting. Stopped at Brownells in Grinnell Iowa while traveling, had Hormady and Winchester but no Remington despite web site saying they did. Of interest, had stacks and stacks of 350 Legend for sale.
Was bidding on a case(100 rds) of accutips on gb, dropped out at $350, sold for $500 plus shipping. Crazy, $5+ a round for slugs.