Very clean images and many of them too, by all accounts that doesn't look like a 30mm chin gun to me, that's probably most likely a 23mm gun
30mm gun and it's associated bullets can end up being quite heavy, lifting 1500 x 23mm or 1500 x 30mm can lead to some considerable weight difference, with the engine power limitation it might be the reason why China picked the 23mm over the 30mm
23mm is still a good calibre