The Killer

Franchi PA3

Used by the syndicate killer.

Ruger Sp100/IDK

Can be seen used by Dumbo and few other police men.

CZ-75

Can be seen in the house shootout use by the gangsters attacking.

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Beretta 92FS

Or its copy, the Taurus PT-92. (Nope: it looks to be a Beretta, plus Chow Yun-Fat doesn't like Taurus guns. He always tries to use Berettas).

The ones in this picture are Berettas, but actually, The Killer features more Tauruses than Berettas. One of the armorers from the movie used to post on a message board I visited, and he says they only had access to one 92F for most of the shoot, so they used Tauruses in many scenes.

In the picture posted, At least one is a Beretta, I can see the Slide-mounted safety.

Beretta 92FS - 9mm.

Beretta M12

Used by Ah Jong and several Triad members in the house shootout

Heckler & Koch MP5K

Ah Jong (Chow Yun-Fat) fires his MP5K.

Colt Commando M733

Used by several of the Triad members in the battle at Fung Sei's house.

(Fake) SVD Dragunov

The rifle used by Ah Jong (Chow Yun-Fat) to carry out his assassination plot is a Chinese Type 56 (AKM) modified to look like a SVD Dragunov.

A real SVD Dragunov sniper rifle for comparison. Note the scope and mount, receiver dust cover, receiver side, magazine type, gas tube, rear stock. All are different than the rifle that Chow Yun-Fat uses. He is using a fake SVD mocked up from a Chinese AK.

Norinco Type 56 mocked up to look like a SVD

M16A2

Used by the first assassin at the beach that tries to kill Ah Jong (Chow Yun-Fat) after the hit on Wong Dung-Yu. The rifle has a scope mounted on top of the carry handle and has a twenty-round magazine.

Uzi

One of the assassins at Ah Jong (Chow Yun-Fat)'s apartment uses an Uzi mounted with a sound suppressor.

AK-47

An AK rifle, possibly a Chinese Type 56-1 with a folding stock, is used in the church shootout.

Browning BDA9/FN HP-DA

Used by several Triad members in the nightclub shootout. Shortly after, it is used once again by Triads, Wong Tong (Wong Kwong-Leung), and Li Ying (Danny Lee) at the gun deal scene and the bus chase. The FN HP-DA continues to be used by Triad members throughout the movie. Near the end, Fung Sei (Chu Kong) briefly commandeers one in his attempt to retrieve Ah Jong's (Chow Yun-Fat) money from Wong Hoi (Shing Fui-On).

Mossberg 500 with wood forend

An Mosseberg 500 with wood forend also leftout a pistol grip can be seen used by Dumbo in the church shootout.

Remington 870 sawed off

Remington 870 can be seen used by some gangsters throughout the movie also by Mickey Mouse while he went akimbo with a Mp5k and his remington shotgun.

Taurus pt92

These can seen use by various of gangster and the main characters with stainless and non or they can beretta inox(not to sure).