Ive started cleaning brass and have come across a number of cases with these indentations on them. They go all the way around, the depths of the indentations vary as they go around. They also vary from case to case. So far about 4-5 out of the dozen or so Ive pulled out of the tumbler have them.

sooty 9mm cases on reloads

Bulk 9mm Ammo In Stock - 124 gr FMJ - 9 mm Luger Ammunition by Military Ballistics Industries For Sale - 1000 Rounds

Who will train them?

Some say 22lr is ineffective. I care to differ. : r/CCW

Bulk 9mm Ammo In Stock - 124 gr FMJ - 9 mm Luger Ammunition by Military Ballistics Industries For Sale - 1000 Rounds

Indentations on 9mm case - Ammunition & Reloading - New Jersey Gun Forums

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Issues when reloading 9mm cases

Continuing on the theme of case head separation. : r/reloading

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Making 40 S&W bullets from 9mm cases

Who will train them?