Coop,
Have you tried any different slugs? I use the Lyman 525 grain in one of my Mossy 500s, and I get 1.5 at 75 yards. Good enough for me as I hunt the Florida swamps in tight cover. The Lyman's are also a bit more economical, too.
BTW, the Hastings barrel is a 1:34 twist rate.
ST762