Neck sizing will fully enable headspacing off the shoulder, rather than the belt. J2Crows is the only person I've ever heard that actually uses the same paper clip method to identify developing case problems, before they become a total case integrity failure. I've never had a belted case fail any where else but above the belt, but that was far more frequent before I started necking years ago.
Primer pockets do get loose after 6 or so cycles, but I find CCI primers have really excellent sealing characteristics. I'm not absolutely sure what is preventing them from leaking, but I've never had one fail in that or any other manner. A long time ago A friend of mine told me because CCIs are beveled on the cup rim, they seal during normal pressure build up as long as they fit tight enough to stay in the pocket after seating them. Considering the high working pressure loads I build, I'm finding some credibility to that explanation.
So far as number of cycles, again, it will completely be dependent on how you load. I don't load for the 300 win. mag. but the 7mm rem. mag is a high working pressure cartridge, and I'm not shy of taking it to it's limits. But even so, it will easily go 8 cycles with softer brass, Remington, and with Winchester or federal brass I get well into 12 cycles or more. I don't know if my loading methods are contributing factors, but accordingly I would think my style would cause premature case failure. my loads are always wroked up maximum powder charges of slow burning powders.
But to answer your question as well as can be. Inspect your brass for exterior and interior signs for initial case separation. Using the sharpened paper clip method to feel for any thing that causes the paper clip to catch on, is a good way to find an interior sign of separation just above, or around the belt. Same on the exterior of the case, look for any cracks developing. I tumble real well after resizing, and then use a magnifying glass to look for initial signs of fracturing. Because the first stages of separation can be easily over looked on a dirty case, I make sure I resize and tumble, inspecting after each of those steps. Not FL sizing in my opinion, makes it easier to spot problems because the case isn't being worked any where but the neck. This eliminates the problem of having to figure out what is resizing marks, and what is separation. I'm considering trying a FL collet die. I've checked into these dies, and apparently they will extend case life substantially longer than even a a neck die will. If I can squeeze another couple of loadings, or more according to what I'm hearing, it may be worth trying it out.
