For 25m centerfire pistol, the caliber may fall between 7.62mm and 9.65mm (.30" and .38"). Rules specify that "high power type 'Magnum' ammunition is not allowed." I'm not sure just what defines "magnum" ammo in their book. I found no definition in the USAS pistol rules.
For 50m pistol and 25m rimfire pistol, 22 long rifle ammo is called for. Rules say that for Rapid Fire Pistol the minimum bullet weight is 2.53g (39 grains), and minimum velocity is 250 m/sec (820 fps).
