The following weapons were used in the film Johnny Mnemonic:
Dan Wesson Model 15 Revolver
Takahashi (Takeshi Kitano) pulls a Dan Wesson Model 15 Revolver when he confronts Johnny (Keanu Reeves)
Dan Wesson Revolver Model 15-VH - .357 Magnum
Pretty (Tracy Tweed) is pulling a Walther PPK.
Walther PPK - 9mm Kurz aka 9x17mm (.380 ACP)
Heckler & Koch MP5A2
The scientists who store the information in Johnny's head are seen using Heckler & Koch MP5A2's when they are confronted by the henchmen of Shinji (Dennis Akayama).
Heckler & Koch MP5A2 - 9x19mm with early "slimline" handguard
A Yakuza soldier is seen using an AT4 to destroy the hideout of J-Bone (Ice-T).
M136 AT4 Anti-Tank recoilless launcher - 84mm
Note AT4 portrayed firing incorrectly. That is actually the rear-end of the AT4, not front.
J-Bone's main weapon is a pistol crossbow.
Futuristic Blaster Pistol
Several characters including Johnny are seen using a futuristic blaster pistol that appears to have parts from a paintball gun.