Thanks, it is coming out quite well now. First three shots are in a 30mm circle now, but the fourth has a habit to fly off at least 10cm. Its almost as if something has come loose, and it has to cool down realy long time before shooting it again (20min isnt enough).

I got to chrono a couple shots today and they are about 1850f/s (1851 and 1849) so they are at the 550m/s i was looking for with a 400grs bullet.