and my unscientific research as shown me that neck splitting on pistol brass, either brass or nickle plate is caused by work hardening the brass.
When I was a Deputy Sheriff I carried a 357 revolver, we used Remington hollow points with nickel plated brass, the ammo that was carried on our belts was shot up every 6 months to make sure we had fresh ammo on our belts. It was not uncommon to have 2 or 3 case splits out of the 30 rounds I carried on my duty belt and in the pistol. New cases splitting on the first firing, I observed that over a period of years, so it wasn't like it was just a certain lot, the ammo was often less than a year old when we shot it up.
6 in the gun
12 rounds in belt loops
12 rounds in speed loaders