Couple of possibilities come to mind. If you originally loaded with as-cast bullets, you could have gotten that much variation. If that ain't the case, you likely have a hardness problem. Dead soft annealed brass has little or no spring back. Another possibilty is that you are as sloppy as I am and keep the brass segregated by lot but not by times fired. If some of it had been fired more often, it would be harder.
Me, I'd either toss it or anneal it, depending on the cost of the brass.