In your panel.cfg (open with notepad) near the top you should have a [VIEWS] paragraph, something like:
[VIEWS] view_forward_WINDOWS=%window_title_00%
VIEW_FORWARD_DIR=2.6, 0.0, 0.0
VIEW_FORWARD_ZOOM=0.85
VIEW_RIGHT_ZOOM=0.85
VIEW_LEFT_ZOOM=0.85
VIEW_REAR_ZOOM=.25
VIEW_FORWARD_UP_ZOOM=0.24
It is the value for VIEW_FORWARD_DIR=2.6, 0.0, 0.0 that you want to adjust to raise or lower the bullet stream in your gunsight. Raise or lower the DIR=2.6 by increments of 0.1 to raise or lower the stream slightly. Save the file, delete any .cdp file in the aircraft folder and give the plane a try, Repeat as necessary until the bullet stream is where you want it.
Use a utility called AimIt to change gun convergence distance.
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