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Fire-formed/trimmed from what to what? Did you trim according to something written in a book or to the chamber for which they are intended? Why shoot a gallery load before a full-power load? Is this a dramatic case change? If the brass is expanding a lot, it will shrink a lot. My problem is most chambers being too long in the neck. I don’t ever recall brass stretching enough to require trimming. If loaded hot, I generally wear out the web first. I also try to work up loads that do not require a crimp. If the neck is not crimped enough to fit inside the throat, you don’t have to worry about over-pressure due to long brass. One thing I always keep in mind is the story of when Quigly Down Under came out and everyone had to have a 45-120. Many people were having brass fail after just two or three loadings. It turns out, they were trimming the brass to minimum length after every shot. That massive bullet inside the brass expanded upon firing and pulled the brass with it as it left, until the case mouth reached the front of the chamber and bottomed out. When they trimmed it back, it would do it again the next shot. If they just let the brass fit the chamber, everything works out fine. I’ve learned it is not always prudent to do things exactly as the loading manuals say (gasp!).
With jacketed bullets, I’ve found that your .008″ too short brass will not hurt anything. If you crimp, you may have issues depending on your crimp die.
What gets me is when you take a loaded cartridge with brass fitted to one gun and fire it in a gun with a slightly smaller chamber. The bolt may take some force to close, but after firing the brass case fits almost like it had been full-length re-sized.