The AP Pistol is a fully automatic pistol featured in GTA V. It is much like the Automatic 9mm from The Lost and Damned.
The gun is seen being used by Michael De Santa during Three's Company, as well as by Franklin, in the official gameplay trailer. It appears to resemble an OTs-33 Pernach automatic pistol from the HUD icon and its in-game appearance. Unlike the Auto 9mm, the AP Pistol is much more accurate, and has a lighter recoil, which can be lightened even more with a suppressor attatchment. It has an 18-round magazine with the option to extend to 36 rounds. Due to its high accuracy, high rate of fire, common ammo, high power, and having a large magazine size (with extended clip) it is arguably the best drive-by weapon in the game. It is all-round superior to the Micro SMG due to the higher rate of fire and slightly higher magazine capacity, however the Micro SMG is the weapon equiped by default during drive-bys, needing several weapon changes to get the AP Pistol, although this can be fixed in GTA Online by simply tossing all other drive-by weapons.
The AP Pistol is most likely not a standard issue FIB weapon, as it is based upon a Russian weapon. Still, the basic Pistol is based on a Brazilian weapon (the Taurus PT92 in this case) and the FIB, as well as the IAA, have it as a standard issue weapon.