I can get really decent groups (never really measured them, as my 452 is my "groups" gun), but I'd say the trigger is the limiting factor, not the barrel. The trigger can be lightened with a flip of the sear spring, which helps a lot. I haven't benched it in a while, but I believe I was shooting sub-quarter sized groups at 40 yards the last time I had it on a rest. If I miss a squirrel, I know to blame myself, not the rifle.
They no longer make the rifle barrel, only the pistol ones, but there are rumors that they will do another run of Buckmark rifle barrels.