The Master Hunter Disc Extreme from all I have read is a fine fine fine rifle!!!! If it is like my Knight rifles, don't be shy with the powder horn. For starters I would get some 250 grain Shockwaves and start with 90 grains of loose powder like nchawkeye said. Work it up from there. Barnes Expanders are what shoots well out of my Knights although they actually shoot well with a number of different things..

Congratulations on the rifle. Keep us posted on how it shoots..