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Yep, gigag04 is correct. IDPA sanctioned competition is divided into five separate divisions.

Autoloaders: Stock Service Pistol (SSP), Enhanced Service Pistol (ESP), and Custom Defensive Pistol (CDP). The minimum caliber for autoloaders is 9mm (9x19). CDP must be .45 ACP.

Wheel guns: Stock Service Revolver (SSR), and Enhanced Service Revolver (ESR). The minimum caliber for SSR is .38 Spl (rimmed-case; no moon clips allowed); the minimum caliber for ESR is 9mm (.355" or larger; a 9x19 minimum is not mandated, but a power factor of 165,000 is, so no .380 ACP or Makarov), rimmed or rimmless cases, moon clips are allowed.

There is a sixth, Backup Gun (BUG) specification in IDPA, but it's defined for club-level matches only; it isn't a valid division for any sanctioned match. A .380 ACP would fit there.

You can find the IDPA rule book at http://www.idpa.com/.