An enlargement of the cartridge case head diameter on firing.
SAAMI Rifle Cartridge Catalog
9mm SAAMI question? - 9mm/38 Caliber - Brian Enos's Forums Maku
Rifle Brass Lifespan - East Coast Reloading Supplies, Inc.
SAAMI Publishes Accepted 12-Gauge 1¾-Inch Cartridge and Chamber
357 Case Head Expansion (77/357)
Cases covered with soot - problem? Please advice!
Can you help me identify a bullet casing? - Quora
Case head separation? Long Range Hunting Forum
Headspace 7mm Rem mag - The Firing Line Forums
Headspace (firearms) - Wikipedia
Case bulge near webbing
When are Pressures Too High? « Shooters Notes