I suspect the brass/ammo if this has not happened previously or now with other brass.

Improperly annealed cases.

If the top barrel is not splitting the necks, measure the fired cases form each chamber to see what the diameters are & how they compare.

I still suspect the brass - they should not be splitting if brand new and previously unfired.

I can also see absolutely no valid reason how or why a 'certain' primer could cause split necks. Increase pressure over other primers - perhaps, decrease pressures, possibly over some other 'hot' primer of course - but to cause split necks - I'm afraid that I find difficult to comprehend.