Back in the '90's, I bought a 1K case of Norinco 5.56mm ammos for my AR. About 1 of every 7 or 8 cases neck-split on firing... this was new, factory ammos. I chalked that up to bad brass alloy, or brass that had somehow work hardened during manufacture.
Shot the same ammo during the same time period in my IMI Galil ARM 392, and don't remember any split necks at all - Guess my (CJ 92 headstamp) batch had appropriate annealing/alloyed brass. I reloaded a lot of it, and did notice however a lot of the extractor grooves were cut kinda wonky. Other than that I consider it very good ammo, full power, boxer primed, reliable, non corrosive and my God what was it, around $70-80 or so for a case? FWIW, here is some chronograph data of it, shot from my Galil's 16" barrel:
3006, 3038, 3073, 3015, 3027
Propellant was a gray ball weighing 27 grains, with the FMJ-BT bullet weighing 54.5 grains.
To the OP, I'll add to the heap - All is well, and you will see many more along the way. In a rifle, I sure don't like to see cracks that go around the case, or a crack like that near the web, but you will see these lengthwise cracks along the sides here as well - Brass is just tired, and needs a permanent rest. Good luck.