I have a Crown Mk2 synthetic stock, with both a 600mm .25 barrel as well as a 600mm .22 barrel. I have installed a barrel band and a 700cc air vessel.
I prefer the .25 600mm as it produces more horsepower and great accuracy shooting the Neilson 29gr slugs at 970 fps. Std .9 over 10 shots.
The 600mm barrel in .22 performs very well shooting the Neilson 26.8 slugs. Same std.
I have heard numerous folks say that they get better accuracy with a higher std, which I disagree with. My theory is when the internal ballistics is in "harmony " with greater velocity consistency, then you can concentrate on tuning for groups with barrel harmonics, not say a slight adjustment to the hammer strike might be needed to achieve those sub moa groups.
Very hard to beat the Mk2, sometimes a bit hard to tune , having to remove the stock to adjust the per-load on the hammer spring but once that is set, it's a dream to shooting, whether hunting or target.
I can harding wait to see the new innovations from the new Pantera to be incorporated into the Mk3!