i had the same problem with the 250gr sst using the old black sabot, and this year i switched to the 250gr sst with the new red low drag sabot, same ballistics as the black sabot and with 75% less loading resistance, plus it shot better out of my sidekick, got a nice 1" 3 shot 100 yard group with a truglo 30mm 5moa red dot.
also i'm shooting 3 pyrodex pellets, i tried 777 pellets but they were dirtier for me, so that could be your problem there, also i remember reading somewhere that hornady claims that lube on the sabot will effect accuracy, dunno if its true or not so you'll have to experiment
also i'm assuming your having problems with the black sabot, if your having problems with the red sabot then i dont know what to tell you