read through the posts on here.  You will need a shotcup with TSS for sure.  Ballistic Products has what you need.  My M/L likes the 15gm/cc #7 but TSS will work too.  If it is possible, threading the barrel for a choke will be a huge difference.  If not, maybe try lead.  I read somewhere about a recipe that does well in more open cylinders.  May have been on here.