Yeah, I've seen the same thing first hand firing various small arms. However, the thing is we have manufacturer data about the precision standards of the weapon when fired in full auto, on the ground, during weapon sight zeroing.
The above Northrup document states that the accuracy standard is 8 mil, 80%. There are actually documents (Cartridges of the World I think?) that show the M39 cannon shooting 1 MOA (aprox 0.25 mil) when it is securely mounted and single fired on the ground, so 8 mil sounds about right for high ROF full-auto.
The issue is that, all pilot error aside, the cannons are currently spraying rounds in a pattern that is so large it would actually be impossible to replicate in real life without the cannon rounds being completely destabilized ,tumbling end over end, and curving wildly all over the place like a US baseball pitcher throwing curveballs.
ETA: Completely jealous of your experience firing a 30mm on an IFV. Fun memories! :D