New PCP owner needs advice on tuning process

I've got four 30 shot string graphs attached using Baracuda Hunter Extreme 18.52 gr pellets. Starting with no hammer spring adjustment, then lightening the spring pressure 1, 1 1/2 and 2 full turns. I'd appreciate it if some tuning experts could give me their opinion of these results. Should I be seeing more of a bell curve, and if so, how do I proceed. Or is one of these adjustments this the best I can do without installing a regulator?
Lamar

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I got a chance to shoot a little. I had shoulder surgery so I could only stare at it for a while. I don't have a chrono and I only have 20yds to play with for distance at my house. Can't go anywhere yet to shoot because I have another week to go of workmans comp. I shot 30 rds of Crosman 14.3 hollow points. Trying to sight the scope was a little bit of a pain until I got to the 18th shot then it pretty much went in the same hole when the pressure went down a little. I would agree that 14.3 is a little light to shoot with a full tank at 2900 psi.