Brass also flows forward as it is used. In my experience softer brass flows more and the neck gets thick as that happens. I have found that older Winchester Super-X brass sometimes did not stretch as much as federal, maybe it was harder? After using those a few times they started cracking, these were only shot and reloaded once. I found this only after trimming and seeing how thick the necks were becoming with each use, thick necks can cause more problems and may need to be turned down, when they get to this point I just throw them away beacuse the case walls get thinner at the same time. I read either here in a posting or in one of Rifles magazines about a way to check inside the case to see if the stretching caused any thinning spots to form. It seemed pretty simple and was checking for rings forming. They were talking about cases breaking off at the base. I like to use Remington brass and Federal brass, I try to keep all of them the same load age for uniformity and check for neck wall thickness as I trim them. The ones that do develope thick neck walls tend to get lighter quicker when I check their weights. It sounded like you had cases of different age. It may be worth it to buy a bag of 100 or so and start with brass the same age and headstamp. I have wondered if there is an advantage to nickel plated brass if it holds up better or not. Maybe someone can answer that for us. Hope this helps, Geo.
