I have an Indian Creek .560 in mine, and I've tried over a dozen shells with it...the 2 top performers have been the hevi 13 magnum blend and Winchester supreme #5's...the winchesters seem to hold a little better pattern in mine...
What kind of numbers are you getting out of that choke? I'm gonna be shooting TSS but need a backup plan if I run out, or I may use store boughts to back up TSS.