Looks like your rifle likes that TTSX a little farther off the lands unless maybe its you, like you said. That 63.1gr with the 2.875 COAL looks perfect to me. The variance is crazy low which is obviously really good. Are you allowing cool down time between shots? The barrels on every wsm I've ever owned heat up really quick.
I find it hard to shoot a "perfect" 5 round group. I have a Tikka 270wsm I can put 4 110gr TTSX's in the same hole at 100yds but for some reason that 5 one always ends up a 1/2" outside the rest. Very similar with the 300wsm I posted the pics of earlier in this thread.
