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...And note there are a very few foreign-made cases where the stretch starts halfway up the side of the case due to thick tapered brass from that point down to the head. Just think: "Shiney ring bad."
 
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Yep. Storage conditions and whether or not a cleaner or some other agent has left the surface activated or has allowed exposure to ammonia. Even small amounts of ammonia from a kitty litter box or damp fertilizer (or from polishing with Brasso) can cause season cracking over an extended period of time.
 
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The Teslong basic borescope can be had for $55 on Amazon, and they work quite well and would be fine for internal case inspection.
 
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There is no single "correct" time and temperature combination for annealing cartridge brass because how much is required varies with how much the brass has been work-hardened. The harder the brass, the lower the combination of temperature and time required to achieve recovery (stress-relieving of the dislocations at the atomic level), or recrystallization. The higher the stress, the less heat it takes to release it and start an avalanche of return to a less stressed state. For example, a 50% work-hardened piece of cartridge brass, at any given annealing temperature, takes something on the order of ten times longer to start recrystallization than a 75% hard piece of brass requires.

Case necks don't usually start to split until they are approaching 100% work-hardening. This means that if you set your annealing process up to provide just enough temperature exposure for just enough time to relieve the stresses in necks that are close to splitting, then apply it every time you reload, it won't do much of anything at first because the brass isn't yet hard enough to respond to that level of time and temperature. So your necks will continue to harden with each reloading cycle until they get hard enough to start responding to that time and temperature exposure. They will start to respond before becoming hard enough to split, but they won't be fully stress-relieved, either. You will end up, in that scenario, with a sort of upper limit to neck stress that you are setting for the brass. This, to me, explains why Bryan Litz's trial with the AMP annealer found no advantage to annealing test cases after every firing as compared to the performance of cases he simply reloaded ten times without annealing.

I have seen it argued that part of Litz's failure to see any effect is that he is shooting in match guns with tight chambers that don't work the brass much, where someone using the 300 WM would see the difference, but I don't know this from experience.

The main thing needed to keep necks from splitting is simply to get through recovery. Recrystallization and grain growth are not required for brass life extension. Toward the no-split objective, metallurgist Fred Barker wrote:

"(1) Lead Pot Method: heat lead to 725°-750°F; dip neck into powdered graphite and then holding body of case in fingertips into molten lead: when case body becomes too hot to hold slap case into wet towel; or
"(2) Candle-flame method: Hold case body in fingertips, place case neck in flame and twirl case back & forth until case body is too hot to hold, then slap case into wet towel; wipe soot off neck & shoulder with dry paper towel or 0000 steel wool."
Fred Barker, Precision Shooting Magazine (RIP), July 1996, pp. 90-92
 
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Try the candle. The torch can be set to push heat into the brass fast enough to get ahead of that heat getting back to your fingers. The candle won't put out enough BTUs to do that. Its only drawback is soot to wipe off.
 
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