Fang Keming (Richie Ren) and officers of the Police Tactical Unit (PTU) use Smith & Wesson Model 10HB revolvers during a scene where Triad members attack a prisoner convoy.
Pistols
SIG-Sauer P228
A SIG-Sauer P228 is seen in the hands of Fang (Richie Ren) during the opening stakeout scene. He uses it to save Chen (Edison Chen) when he had trouble trying to deal with several machete-wielding Triads.
Beretta 92FS
Triad leader Tao (Jack Kao) is armed with a Beretta 92FS during a flashback sequence and later during the shootout in the elevator. Other characters are also armed with the 92FS.
Walther P99
A Walther P99 is carried by Er Ge (Kai Chi Liu) during the elevator scene, later drops it when shot in the arm by Chen (Edison Chen). Fang (Richie Ren) also obtains one during the elevator scene.
Glock 17
A Glock 17 is briefly seen in the hands of Ching (Huang Xiaoming) during the elevator scene.
Heckler & Koch MP5A3 submachine guns are used by the HKPF Special Duties Unit (SDU) throughout the film. They are also used by one of the PTU officers guarding a prisoner convoy and by another officer during a shootout at Ching's apartment.
Heckler & Koch MP5A2
A Heckler & Koch MP5A2 is used by one of the PTU officers guarding the prisoner convoy.
Steyr TMP
A Steyr TMP, distinguished by its fixed detachable stock, is used by one of the Triads who ambushes the prisoner convoy.
Assault Rifles
M16A1
Several M16A1 rifles (with A2 handguards) are used by SDU snipers during training sessions.
M16A2
M16A2 rifles are seen during the sniper training sequences.
M16A4
An SDU sniper shot by Ching is armed with an M16A4.
Custom M16
A custom M16 is used by SDU snipers, consisting of an A1 upper receiver (identifiable by its teardrop forward assist and lack of a brass deflector) with the carry handle machined off and converted to a flat top, and an A2 profile barrel.
Remington 870 shotguns are seen in the hands of PTU officers guarding the prisoner convoy when they are ambushed by the Triads.
Sniper Rifles
Heckler & Koch PSG-1
The Heckler & Koch PSG-1 sniper rifle is prominently used by Chen (Edison Chen) throughout much of the film, and by Ching (Huang Xiaoming) in flashback sequences. The rifle itself is a fake that was created by combining a long barrel with a PSG-1 forearm, buttstock and pistol grip on an HK91/G3 body, similar to the H&K SR9 rifles seen in Hollywood productions.
Tokyo Marui PSG-1 (AEG)
For non-firing scenes, characters use an airsoft PSG-1, made by Tokyo Marui.
Remington 700 AICS
A Remington 700 rifle in an AICS stock is used by Shane (Bowie Lam), one of Fang's fellow SDU snipers.
Heckler & Koch G3SG/1
Several members of the SDU sniper team are armed with Heckler & Koch G3SG/1 rifles. Note that this is just a standard H&K G3 that's made to look like a G3SG/1 rifle. Although it's fitted with an SG/1 stock, it lacks the set trigger that's characteristic of factory SG/1 rifles.
Mk 12 Mod 1 SPR
Suppressed Mk 12 Mod 1 Special Purpose Rifles with Harris bipods, 20-round magazines and no iron sights are used by Fang and Chen, notably during a scene where Chen attempts to replicate Ching's shots and during the finale.
Norinco Type 85
Ching (Huang Xiaoming) uses the Norinco Type 85, a Chinese copy of the SVD Dragunov, as his primary sniper rifle throughout much of the film.
Barrett M82A1 (Mock-up)
In the finale, Ching uses a Barrett M82A1 alongside his Type 85, engaging in a lengthy duel with Fang, Chen and the rest of the SDU sniper team. We could note that between the moment when he is filmed from his back and from his front, his rifle switches from a G3SG/1 to the Barrett M82A1. In the French version, Fang says Ching is using a 50 millimeters as opposed to .50 inches.
Also, this prop gun appears to be a mock-up incorporating a SKS rifle receiver.
Other
M26 Hand Grenade
Tao (Jack Kao) is armed with an M26 hand grenade during a flashback sequence.