Is there something about the guns in those two planes that make them easier to use?
yes - stability.
you tried the F4u. the hog suffers from some instability in the yaw direction. notice that when you roll it the nose swings left and right when you stop.
Other planes have a nasty "nose bumping" effect (try the yak).
the N1k is a very smooth flyer, and although the balistics aren't much, the ease of stabling the piper on the target and the fact that you have 4*20mm (only need 2-3 hits) makes the gunnery easier.
Bozon