OK, I checked my sight alignment again and guess what? You were right, lurkingknit. My outer barrel is at an angle to the line of sight. Not much but visible. At 8m the barrel is looking about 10 cm gto the left of the point of aim. Just like the bbs impact.
Please let me know if i should look for a rear sight to compensate by more windage adjustment or take off the outer barrel and re-align. I woud go with a new rear sight or optical sight but it should go way more to the right than the stock one on the gun and I am not sure if that is possible.
Happy shooting, and hopefully straight!