If it's a "custom" gun, there's no telling what you'll get. If the trigger group has been futzed with, try replacing the springs with OEM and see if they will do better. If a lighter recoil spring was installed to be more "reliable" with lighter ammo, try switching back to OEM on that as well. On several occasions I watched Tom Knapp shoot extremely fast splits (no I didn't have a timer but I know what I saw) with his bone-stock M1's and M2's. Ten hand-thrown clays requires a fast action. Among other things.
Just curious: What are you shooting that calls for less than .2 splits with a shotgun?