Way back when I used to do this risky stuff, we experienced quite a few such incidents. A couple of Harrier losses at Holbeach were most likely due to ricochet. One was fatal, suggesting that the pilot took the 30mm ball round. I suffered minor airframe ricochet damage in both Harrier and Jaguar, both only noticed after landing.
A significant factor on the range was the accumulation of dead rounds in the ground around the target. If a fired round hit a lying one, either could jump into the air just before the firing aircraft passed quite low over the target as it recovered. It was very important that the target area was regularly raked clean of old rounds. It was also unfortunate that we often had right-hand range patterns, and the Aden spun the round clockwise, making it possible to collect someone else’s round downwind.
With HE, ricochet was less of a problem, although it was wise to remember if firing at a splash target that the first few rounds cocked in were ball, which skim quite nicely off water. Premature detonation was a risk, and was sometimes visible not far in front of the muzzle. That didn’t feel too bad when you got used to it with the low-mounted guns in the Harrier and Jaguar, but I hope that the F35A’s neat shoulder mounted gun has more reliable ammunition.