Zero the rifle at say 40yds, refill to 190Bar, and left off numerous shots at the same zero point & note where the best grouping is. If they are all the same apart from when the power drops off, your optimum fill pressure will be 190Bar, if it starts low or high then the fill will be lower. (e.g. if the zero moves after say 10 shots, then approx 175Bar is the optimum).