Minimum Caliber for Open Division is 9mm.   The pistol is allowed to be compensated and barrels may be ported.  Pistols are usually "double-stack" single action autos.  There is no limit on magazine capacity and pistols may have optical sights.  Race-type holsters are used and there are no restrictions on holster or magazine pouch position.  Common brands used in Open Division are  STI, SVI, Paraordnance, and Tangfolio.  This is division can be compared to "formula-one" racing.