I made this THING to shoot well!
560 gr solid bulet in paper patch over greese cookie and over 165 gr of BP "White Bear" #3 (FFFg) was too tough for it. Left bbl shot to the left and right - to the right, distance between POI's was abot 8" at 50 meters.
Next reloading and 520 gr HP bulet, paper patched, greese cookie, 158 gr of BP and you can see two control shots at the target (sorry, for the target, got no time to print something more good-looking).
I think this HP bullet and 160 gr of BP will be what I expected.
Next step is testing in wild.
Will be continiued