If you decide to shoot loose 777 DON'T go over 120 to possibly 125 grs of loose 777, that is a max load as 777 loose is about 15% more powerful than the same grain charge in pellets. The pellets are equil to 150 gr of loose black powder or Pyrodex, not loose 777. The loose is only more accurat if you take the time to work up a load 5 grs at a time.
I think you will find your scope is set up for 150 grs of 777 pellets and a 250 gr Shock Wave bullet. The XTPs have a lower BC ( because of the fairly blunt nose ) the XTPs will hit lower at long range than the SSTs or Shock Waves (Same Bullets just different sabot).