Brass gets hardened by "working". Repeated sizing and firing will eventually harden the mouth area to the point it splits. .38 Spl will do this gernerally after about 6-10 loadings. If the brass was once fired sometime after WWII, it is still once fired and fine. Anealing to remove the work hardening is a PITA for somthing like .38 Spl. Shoot it till it splits and recycle it.
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