I shoot a Marlin 512 Slugmaster bolt gun (28″ fully rifled barrel), scoped with a Bushnell Trophy 1.75-4.5 x 32. I have found the Winchester Supreme Partition Gold 2 3/4″ to be the most accurate through this set-up. The 3″ Partition Golds sound like a good idea, but they were a little less consistent and “only” 100 FPS faster. I’ll “sacrifice” speed for accuracy.
I’ve also tried the Hornady SSTs, and they were pretty wild through my bolt gun. My uncle had the same problem with ’em through his Remington 870 with a fully rifled barrel and open sights.
Maybe the Hornadys would be okay through an autoloader because they’re so wild and inconsistent you’d be better off to just “spray and pray”.
Jusy my .02