When the revolver is seen in hands of Eric (Andrew J. Ferchland), Zack Grant's son, it is definitely another item. It differs in several details (full length underlug and other), and Eric holds a heavy revolver very steady for a seven year old boy. This revolver is most likely a lightweight prop or even a toy gun.
Pistols
SIG-Sauer P226
Many characters are seen with SIG-Sauer P226 pistols including Zack Grant (Russell Crowe) and other FBI agents, Yakuza and Serlano's thugs.
Several of Serlano's thugs are armed with Beretta 92FS pistols during the firefight in Yakuza hideout. In the beginning of the final scene Yuji Kobayashi's (Etsushi Toyokawa) SIG-Sauer P226 switches to Beretta 92FS in a continuity error.
Intratec TEC-9 Mini pistols are seen in hands of several of Serlano's thugs.
Composite Pistol
The Composite Pistol is used by "Mr. Contingency" (Kristopher Logan) and Zack in the Boeing 747 and during the ensuing chase. This appears to be the same weapon that was used by John Malkovich in the 1993 film In The Line of Fire. Though the blank firing version was destroyed after the filming of In The Line of Fire, the pistol used in this movie appears to be the non-firing stunt prop (as Grant fires the pistol twice but both times off-screen).
Submachine Guns
Uzi
Several Serlano's thugs are armed with Uzi SMGs during the firefight in Yakuza hideout.
MAC-11
Several Serlano's thugs are armed with MAC-11 SMGs during the firefight in Yakuza hideout and in several other scenes.
Ingram Machine Pistol Non Gun
Several Serlano's thugs are armed with customised Ingram Machine Pistol Non Gun SMGs. In the final scene Yuji Kobayashi (Etsushi Toyokawa) is armed with this weapon but he is never seen firing it. Only one such weapon can be seen at each moment so it looks like that only single prop is used in the movie though it passes from character to character.
In one scene a CHP officer (Todd Jeffries) is seen with a shotgun that is supposed to be a Remington 870. His shotgun is then used by Yuji Kobayashi (Etsushi Toyokawa). The Remington also appears to be the pump action shotguns seen in the hands of FBI agents during the shootout at Eagle Rock.
Assault Rifles
AK-47 style assault rifle
An AK-47 style assault rifle is used by Yuji's bodyguard Tetsuro (Kyûsaku Shimada) during the shootout at Eagle Rock. It can be some version of Norinco Type 56 but its stock differs from any weapon of AK family. The rifle is seen only through the thick dust.
Poly Tech AKS-47
A Poly Tech AKS-47 style assault rifle is seen in a pile of different firearms in the car of Serlano's thugs during the scene at Eagle Rock. This weapon can be identified due to its typical folding stock. It is never used in action.
Other
M26 hand grenade
An M26 hand grenade is seen on the table of Victor Serlano (Ian Ziering). Next moment it switches to a Mk 2 in a continuity error.
A pile of different firearms is seen in the car of Serlano's thugs during the scene at Eagle Rock. It includes several pistols and revolvers, a MAC-10 or MAC-11 SMG, a Poly Tech AKS-47 assault rifle (it can be identified by its typical folding stock), an M16 style assault rifle and several shotguns.