RE: TC Black Diamond
100 grains of powder and a 250 grain Shockwave will normally shoot real well. I also have the XR model. With pellets I shoot three of them with a Shockwave and it does well. With loose powder I load 120 grains of Goex 2f or 110 grains of Triple Se7en 2f with the Shockwaves.
Some other good shooting projectiles I have found are the 375 grain Buffalo Bullet SSB, Nosler Partitian 260 grain, 300 grain Hornady XTP in an crushed rib sabot, 460 grain .503 diameter No Excuses conicals with 80 grains of powder under them...
If you're shooting off a rest, make sure you are rested on the stock and not the barrel. When I was shooting before off the barrel it would not hit anything... Also be sure and swab between shots.