In addition to coordinated flight exercises with your rudder, another good one is to practice "shooting with your feet" to get a feel for your rudder input and scaling.
One good exercise for this is what I call the "shoot around the clock" exercise:
1) Bring up the target at your current convergence range .target [range]
2) Get up to a cruising speed where your pipper is roughly level with the center of the target
3) When centered, fire a short burst (1-2 seconds), making sure you are unloaded and not maneuvering
4) This is your "test bullet dispersion pattern" - about a tight a pattern as you'll get at convergence
5) Then maneuver to shoot at each of the "clock" points 12:00, 3:00, 6:00 and 9:00 on the target, where the lines meet the outer circle
6) You can do this with our without a lot of rudder use -- but for your rudder practice, try using rudder to aim the pipper precisely on the point where the lines and the outer circle meet before shooting
7) Practice it until you can do all 5 shots (including the center) with a 2 second burst at each, in under 25 seconds with precisely aimed tight bullet patterns
8) Change the order; go counter-clockwise, go from 12 to 6 then 3 to 9, try different variations
Things to note during this practice about rudder specifically:
1) Note how much or how little precise control you have in "aiming with your feet" using rudder - you can scale your rudder axis accordingly
2) Notice that if you rudder and then release just before firing, there will be some wobble as your plane yaws back and forth to center and your shot pattern will be spread horizontally.
3) Notice that if you rudder a little and hold it when you shoot, you may get less "wobble" and a tighter bullet dispersion pattern.
This is one of a series of exercises I do to get a feel for gunnery with different aircraft.
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